American oil beetles may not be the most well-known insects, but they can still be quite fascinating for those who are curious about their habits. These large, flightless beetles can be found throughout the United States, and understanding their diet can give you a better appreciation for their role in the ecosystem.
You might think these beetles feed on oil, given their name. However, the name “oil beetle” actually refers to the oily substance they secrete as a defense mechanism when threatened. In reality, American oil beetles feed primarily on plants and their blossoms. These insects play a vital role as pollinators, helping plants reproduce by spreading their pollen, and they consume plant tissue for nourishment.
As these beetles grow from larvae to adults, their diet changes and adapts accordingly. It’s essential to understand their dietary habits at different stages of their life cycle. In their earliest stage, the larvae consume other insects like aphids and grasshoppers, giving them a vital protein source for growth and development. As they mature into adult beetles, plants become their primary food source.
Understanding the American Oil Beetle
The American Oil Beetle, also known as Meloe americanus, is a flightless beetle that is quite interesting to observe. Its distinct features make it easy to identify.
These beetles are generally black or dark blue, but sometimes may appear as dull black or shiny black. Their size varies, and their abdomen is quite prominent, giving them a unique appearance compared to other beetles. The bumpy texture of their body is another noticeable characteristic.
When it comes to identifying American Oil Beetles, here are the key features to look for:
- Black or dark blue color
- Prominent abdomen
- Bumpy texture
As for what these beetles eat, they primarily feast on plant material as a vital part of their diet. They prefer certain plants like the leaves of wild mustard, for example.
In conclusion, be on the lookout for these distinct features to easily spot an American Oil Beetle, and remember that they are mostly herbivores, enjoying plant-based meals.
Habitat and Distribution
The American oil beetles live primarily in North America, with a wide range of habitats. They can be found across both the United States and Canada. Although these beetles thrive in different environments, they are commonly found in open areas such as grasslands.
In their natural habitat, you’ll notice that these beetles favor regions with ample vegetation and loose soils, which makes it easier for them to burrow and lay their eggs. Apart from grasslands, you can also find them in fields, meadows, and gardens.
To summarize, American oil beetles inhabit:
By understanding the habitat and distribution of the American oil beetles, you’ll have a better grasp of their ecological niche and the environmental conditions that support their existence. So, keep a lookout for these fascinating creatures when you venture into the open areas in North America.
The life cycle of the American oil beetle includes several stages, such as egg, larva, pupa, and adult. This process is known as metamorphosis1. Let’s briefly go through each stage of their life cycle.
In the initial stage, female oil beetles lay approximately 1,000 eggs. These eggs hatch after a specific period, usually in spring2. The larvae that emerge from the eggs are known as triungulins. These tiny, active creatures have three pairs of long legs and are known to be parasitic. They seek a host, such as a solitary bee, and hitch a ride back to the bee’s nest. There, they consume the bee’s eggs and the stored pollen and nectar.
As larvae grow and progress through several instar stages, they eventually molt into their pupa stage. In this stage, they are immobile and undergo physical changes as they prepare to become an adult beetle3. This process can last for about a week.
When the pupa stage is complete, the adult American oil beetles emerge, ready to mate and continue the cycle4. These beetles are usually most active during the spring and early summer seasons5. Adult beetles typically feed on flowers and foliage. However, their main purpose is to find a mate and reproduce, ensuring the survival of their species.
American oil beetles, also known as blister beetles, have a varied diet. In their larval stage, they primarily feed on bees and insects. As adults, their diet consists mainly of plants and flowers. Your garden may become a feeding ground for these beetles.
In the early stages of their life, American oil beetle larvae, called triungulins, are parasitic on bees. They hitch a ride on bees when the bees visit flowers for nectar or pollen. Once inside the bee’s nest, the triungulins feast on bee eggs and larvae. Insects make up a significant portion of their diet at this stage.
As they mature, American oil beetles transition to a more plant-based diet. They are known to consume various flowers, grasses, and leaves in your garden. For example, they may feed on roses and peonies. This feeding habit can cause damage to your plants and affect their growth.
Here’s a table comparing the diet of American oil beetles at different stages of their life:
|Larvae||Bees, Insect eggs|
|Adults||Plants, Flowers, Grass|
To summarize, the diet of American oil beetles varies depending on their stage of development. In their larval stage, they feed on bees and insects, while as adults, their diet consists mainly of plants and flowers. Knowing this information can help you protect your garden from these pests and maintain its overall health.
Relationship with Bees
American oil beetles have an interesting relationship with bees. These beetles mainly rely on bee larvae for their nourishment. To access their food supply, the female oil beetles lay their eggs near the entrance of ground bee nests.
- When the eggs hatch, the beetle larvae wait at the entrance of a ground bee nest.
- They release pheromone signals to lure their future hosts.
Once a male bee arrives, the beetle larvae quickly attach themselves to it. The male bee unknowingly brings the larvae back to the hive, where they come into contact with female bees.
- The larvae find their way onto female bees.
- Female bees carry the larvae back to their own nests.
In the bee nests, the beetle larvae feed on the bee larvae and stored food reserves, which sustains their growth until they complete their development into adult oil beetles.
- The adult oil beetles do not eat.
- Their sole purpose is to reproduce and continue the cycle.
The relationship between American oil beetles and bees is not entirely harmful. Despite feeding on bee larvae, oil beetles do not typically cause significant harm to bee populations. This fascinating relationship highlights the complex dynamics that exist between different species in the natural world.
American oil beetles, also known as blister beetles, have a unique defense mechanism when they feel threatened. They release a chemical called cantharidin from their joints, which causes a blistering effect on the skin.
This defense mechanism is effective in warding off potential predators. Cantharidin is a caustic substance that can cause swelling and blisters when it comes into contact with the skin or mucous membranes. For example:
- If a predator tries to eat a blister beetle, the cantharidin will cause irritation and pain in their mouth and digestive system, discouraging them from consuming the beetle.
The source of this defense chemical is the beetle’s hemolymph, a fluid that is similar to blood in vertebrates. When the beetle is threatened, it will excrete this hemolymph, releasing the cantharidin.
It’s important to be cautious around these beetles, as their defense mechanism can also be harmful to humans. Accidentally crushing a blister beetle can cause the cantharidin to be released, potentially causing painful blisters on the skin.
Blister beetles can be found in various habitats, including alfalfa fields and areas where potatoes are grown. These beetles feed on leaves and flowers, but they don’t typically consume the crops themselves.
In conclusion, the American oil beetle’s defense mechanism of releasing cantharidin is a fascinating and effective way to deter predators. However, it’s important to exercise caution around these beetles, as their defenses can also be harmful to humans and other animals.
Implications for Humans
American oil beetles, also known as blister beetles, feed primarily on plant materials and can be particularly harmful to crops and gardens. However, their potential impacts extend beyond damage to plants.
If you accidentally encounter an American oil beetle, you should be cautious. When threatened or crushed, these beetles release a substance called cantharidin, which can cause:
- Skin blisters
- Irritation or burns
It’s crucial to avoid handling or coming into direct contact with these beetles to prevent these uncomfortable symptoms.
Although not common, in some cases, exposure to cantharidin may result in more severe symptoms, especially if the substance is ingested. This could lead to:
- Stomach pain
If you experience any severe symptoms after coming into contact with an American oil beetle or suspect cantharidin poisoning, seek medical help immediately.
Damage to Plants
The primary diet of American oil beetles consists of leaves, flowers, and other plant parts, posing a threat to your garden and plants. They can cause considerable damage to:
- Ornamental plants
- Agricultural crops
Keep an eye on your plants for any signs of beetle infestations, and consider using environmentally friendly pest control methods to prevent damage to your garden or crops.
By understanding the potential risks associated with American oil beetles, you can take necessary precautions to protect yourself, your loved ones, and your plants from harm.
The Genus Meloe
The Genus Meloe, also known as American oil beetles, belong to the class Insecta, order Coleoptera, and family Meloidae. They are a unique group of beetles that have distinct characteristics and behaviors. In this section, we’ll discuss what these beetles eat and some examples of different species within this genus.
They are commonly called Blister Beetles because of the defensive oil they secrete. When this oil comes into contact with your skin, it can create painful blisters.
- Primary diet: Meloe beetles are known for their unique feeding habits, focusing mainly on the eggs of grasshoppers.
However, as larvae, they have a parasitic relationship with ground-nesting bees, feeding on bee larva and their pollen and nectar provisions.
The Meloe Proscarabaeus, or buttercup oil beetle, is one species within the Meloe genus. This beetle has black shiny body and is often found in places with a high density of its preferred food, the buttercups.
Violet Oil Beetle
Another species within the Genus Meloe is the violet oil beetle. Known for its violet-blue hue, this beetle also preys on grasshopper eggs and parasitizes on bees.
In some cases, Meloe beetles can be considered pests, as their larvae may affect the population of ground-nesting bees. Insecticides can be used to control their numbers, but this method should be used carefully to avoid harming non-target organisms.
Remember that managing these beetles requires a mindful approach, as it’s essential to maintain a balance that supports healthy ecosystems.
Saving the American Oil Beetle
American Oil Beetles, also known as blister beetles from the Meloe genus, are a unique group of beetles that play a significant role in our ecosystem. To save these remarkable creatures and ensure their survival, it is essential to know what they eat and how they contribute to the ecosystem.
Understanding the Diet of American Oil Beetles
American Oil Beetles mainly feed on plant materials, such as leaves and flowers. However, their diet may vary depending on the species. By preserving their natural sources of food, you can help maintain their population.
Predators and Natural Threats
Oil beetles face several natural threats such as birds, reptiles, and small mammals which prey on them. Some predators include:
- Birds like robins and sparrows
- Reptiles like lizards and snakes
- Small mammals like shrews and mice
To protect oil beetles from these threats, create a safe habitat in your garden or backyard by planting a variety of native plants. These plants will provide them with adequate shelter and food sources.
Population Challenges and Conservation Efforts
The American Oil Beetle population is currently facing a decline due to habitat loss, pesticide use, and invasive species. To help conserve these beetles:
- Limit pesticide use in your garden
- Remove invasive plant species
- Provide a suitable habitat by planting native plants
By following these guidelines, you can contribute to the conservation of the American Oil Beetle and help maintain the balance in our ecosystem. Remember, every creature plays an essential role, and even small efforts can make a significant difference.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Oil Beetle from Crete
large black beetle?
Location: Crete, Greece
April 3, 2011 1:40 am
I found this large insect about 500 ft elevation in Crete, Greece while hiking with some friends. I thought it was a Beetle at first but it lacked a split shell that covered wings. it’s ”shell” appeared to be just a large abdomen. i couldn’t tell if it was hard or soft because i didn’t want to risk injuring the bug if it was soft or me if it could bite.
This is a Blister Beetle in the genus Meloe, commonly called an Oil Beetle. The Oil Beetle, like other Blister Beetles, secretes a compound known as cantharidin that can cause blistering of the skin.
Letter 2 – Mating Oil Beetles in Canada
Blister beetle love
Location: Westport, Ontario
October 7, 2010 10:00 pm
My wife and I came across these blister beetles getting some action at our cottage near Westport, Ontario, just north of Kingston. I guess the larger is the female, and she will likely store the sperm until spring, at which point she will allow fertilization to occur and get to the business of laying eggs. Any thoughts on if that is close? And any chance that you recognize the species? Thanks,
Signature: Ian in Ottawa
Your Blister Beetles are Oil Beetles in the genus Meloe, also known as Oil Beetles. BugGuide indicates that there are 22 species in the genus, but there is no explanation on how to identify them or how to distinguish them from one another. With that said, we do not feel qualified to identify this amorous pair to the species level, but we will not give up on getting an answer for you. At the end of the “browse” section on BugGuide, which can be used to further narrow the identification on an insect by moving more thoroughly through the taxonomy, often to the subspecies level, is a page that is called “images seen and deemed unIDable by Dr. Pinto“. This piqued our curiosity, and we decided to try to find out more about this expert in the genus Meloe. Our search toward the identity of Dr Pinto led us the first page of an online journal article entitled The Sexual Behavior of Meloe (Meloe) strigulosus Mannerheim written by John D. Pinto of the University of California, Riverside. On the UC Riverside website, we learned that Dr. Pinto is a Professor of Entomology, Emeritus, and there is a contact email address for him, so we will attempt to get an answer from him regarding the species of your Oil Beetles.
The life cycle of Blister Beetles is very interesting and complicated in that the larva undergo morphological transformations that are more complex than other beetles. There is a mobile larval stage known as the triungulin, and later instars are more sedentary. The Featured Creatures section of the University of Florida Entomology Department has an excellent page on the life cycle of Blister Beetles. The larvae of the Blister Beetles in the genus Meloe live in the underground nests of solitary bees, and BugGuide has a detailed explanation of the life cycle of the larvae, including this information:
“In at least one Meloe species, the larvae climb to the top of a grass or weed stalk as a group, clump together in the shape of a female solitary ground bee, exude a scent that is the same as, or closely resembles, the pheromones of the female bee, and wait for a male ground bee to come along. When he does, he tries to mate with the clump of larvae, whereupon they individually clamp onto his hairs. He then flies away, finds and mates with one or several real female bees, and the larvae transfer to the female(s).
Each impregnated female bee then flies off and builds one to several nests in burrows she digs in the soil, and the larvae transfer again to the new nests. The female bee stocks these nests with honey and pollen for her own young, but the hungry blister beetle young are there to gobble up the provisions. They eventually pupate and finally emerge as adult flightless beetles. Brothers and sisters find each other and mate, produce eggs and the hatchlings start the process all over.
Then there are male beetles from a couple other beetle families who seek out blister beetles, climb onto them and lick off the cantharidin the blister beetles exude. Not only have these other beetles developed a resistance to the cantharidin, they use the blistering agent to impress a female of their own species who then mates with them, whereupon most of the cantharidin is transfered to the female in the form of a sperm packet. The eggs the female subsequently lays are coated with cantharidin to protect them from being eaten before they hatch.“
Alas, we cannot with any certainty respond to your question regarding the storing of the sperm by the female, but most solitary bees are active in the spring and not in the autumn, so your guess seems sound. Perhaps Dr. Pinto can provide additional information should he respond to us.
Ed. Note: Here is our email to Dr. Pinto
Dear Dr. Pinto,
My name is Daniel Marlos and I have no entomology background, nor any scientific credentials for that matter, but that has not stopped me from maintaining the What’s That Bug? website since 2002. Through my pop culture website, I hope to encourage the web browsing public to appreciate the wonder of the lower beasts and to help them understand the important place insects and other bugs occupy in the complex ecosystems of our fragile planet. Someone sent in photos from Ontario yesterday of mating Meloe species and would like them identified and I found you by searching BugGuide and then following some search threads to your profile on UC Riverside. If you could identify the species in these photos, it would be awesome, but even more, if you could provide any information on this question posed by the person in Canada who took the photos: ” I guess the larger is the female, and she will likely store the sperm until spring, at which point she will allow fertilization to occur and get to the business of laying eggs. Any thoughts on if that is close?” I have been unable to locate any information on whether the female hibernates or if she lays eggs that overwinter. Any assistance would be greatly appreciated.
Dr. Pinto Responds
The Meloe photo is of Meloe impressus Kirby, a relatively common species in autumn in certain parts of North America. Females of this species lay their eggs relatively soon after mating, and the eggs overwinter and hatch the following spring. Actually it is more accurate to say that the first instar larva develops rather quickly but doesn’t break out of the egg until spring – at least that is what happens in the lab. Minor point but I might add that it is not entirely clear if the beetles in the photo had mated or not. After successful mating the pair lines up in an end-to-end position for one or two hours. The male in your photo was either still courting or in the first stage of mating before assuming a linear position. Much of what is known about North American Meloe can be found in — Pinto, J. D. & R. B. Selander. 1970. The bionomics of blister beetles of the genus Meloe and a classification of the New World species. Illinois Biological Monographs, #42. Only 1 new species has been described since 1970.
Sincerely, John Pinto
Letter 3 – Mating Oil Beetles
Attached is a photo I took of some beetles around the first of October. There were literally hundreds of them mating on that particular day. I haven’t seen them before and the next day they were gone. The location is in Southern Ontario, Canada (Toronto) and the landscape is close to a river and in one of the last remaining Oak Savanahs in Canada. Our concern is that in Western Canada there is an infestation of Long Horned Asian beetles which has been killing many trees. We hope these are not related. Please identify and reply at your earliest convenience. Thanks in advance,
These are mating Oil Beetles or Short Winged Blister Beetles in the genus Meloe. There is some very interesting information found on BugGuide regarding these beetles including this by Jim McClarin: “Meloe life cycle can be very complex In at least one Meloe species, the larvae climb to the top of a grass or weed stalk as a group, clump together in the shape of a female solitary ground bee, exude a scent that is the same as, or closely resembles, the pheromones of the female bee, and wait for a male ground bee to come along. When he does, he tries to mate with the clump of larvae, whereupon they individually clamp onto his hairs. He then flies away, finds and mates with one or several real female bees, and the larvae transfer to the female(s). Each impregnated female bee then flies off and builds one to several nests in burrows she digs in the soil, and the larvae transfer again to the new nests. The female bee stocks these nests with honey and pollen for her own young, but the hungry blister beetle young are there to gobble up the provisions. They eventually pupate and finally emerge as adult flightless beetles. Brothers and sisters find each other and mate, produce eggs and the hatchlings start the process all over. Then there are male beetles from a couple other beetle families who seek out blister beetles, climb onto them and lick off the cantharidin the blister beetles exude. Not only have these other beetles developed a resistance to the cantharidin, they use the blistering agent to impress a female of their own species who then mates with them, whereupon most of the cantharidin is transfered to the female in the form of a sperm packet. The eggs the female subsequently lays are coated with cantharidin to protect them from being eaten before they hatch. Then there are the bipedal primates who use cantharidin from blister beetles to manufacture the notorious date rape drug, Spanish Fly… “
Letter 4 – Mating Oil Beetles
Beetles doing the deed
I found several of these beetles chewing on leaves of the Wood Anemone flower/plant. They are about 1 1/2″ – 2 ” long. The location is the Upper Peninsula of Michigan, close to the S. shore of Lake Superior. In the one photo, there is another smaller beetle attached to the one eating. I guess these crafty critters are pretty advanced as they can do at least two things at one time! Wish the photo had captured it better but I had to give them a little privacy. So, can you help me identify them? Thanks
Your beetles are a species of Blister Beetle, in the genus Meloe, commonly called Oil Beetles. This seems to be a common habit among Blister Beetles, eating and procreating simultaneously.
Letter 5 – Mating Oil Beetles
Blue metallic Beetles mating
Mon, Nov 3, 2008 at 12:30 PM
I found a half dozen pairs of shiny, slow moving beetles in my friend’s
lawn late this summer. Any idea what these are or will become? They were about 1-1.5 inches long and a bit bigger around than an average Sharpie marker. Thanks!
Looking for bugs in NE
Oakland, Maine,northeastern United States
These are mating Oil Beetles, Blister Beetles in the genus Meloe.
Letter 6 – Bug of the Month December 2009: A Pair of Oil Beetles
November 20, 2009
I found these 2 handsome beetles while digging in the garden in NE massachusetts in early november; I think they were a couple of inches down. I thought they were dead, and placed them in a container for later ID, and when I came back to them a few hours later, they were climbing all over to get out. So, I photographed them, and released them back into the garden. Are they a male and female, and what are they?
Linda in Mass.
These are Oil Beetles in the genus Meloe. Oil Beetles are Blister Beetles and they should be handled with care as they exude a compound that may blister skin. They do appear to be a pair, with the female being the larger of the two individuals. These are really great photos.
It is the first of December, and we hadn’t prepared in advance for a Bug of the Month, so we searched through recent postings and arrived at this lovely pair of Oil Beetles that was submitted last week. Oil Beetles can be found throughout North America, though our sightings from the east are more common. It may be getting a bit late in the year in New England, but they will still be active in the southern portions of their range. According to Bugguide, the antennae of the smaller males are modified as this set of photos indicates. The Oil Beetles release an oily substance that contains cantharidin which can cause blistering in skin, hence the common name of Oil Beetle. This trait is shared with many other Blister Beetles in the family Meloidae, including the notorious European Spanish Fly.
Letter 7 – Mating Oil Beetles
Short Winged Blister Beetle Love
Location: South Jersey
April 28, 2011 11:29 am
Hey I don’t know if you have a picture of the Oil Beetle in the Bug Love area but I took this in my driveway this morning. Kinda looks they are looking at camera.
Signature: Christian M.
We do have several mating Oil Beetle images in our archives including this tragedy, but we can never get too much Bug Love. Thanks for your submission. We have begun receiving some marvelous Blister Beetle images from the Southwest where their diversity is quite astounding.
Letter 8 – Mating Oil Beetles
Subject: mystery bug
Location: sonoita .az
July 22, 2012 9:08 pm
well I live in sonoita arizona. and I was just walking down my path to it my pond and I noticed these 2 beetles and I don’t recognize them at all, they look like they’re wasps but I don’t know what to make of it
Signature: fletcher green
These are mating Oil Beetles, a group of Blister Beetles in the genus Meloe. According to BugGuide, there are at least 22 species in North America, but they all look so similar we are not capable of distinguishing one species from another. Most of our reports come from eastern states, however, BugGuide does have reports of western state sightings including this Meloe barbarus from Tuscon, Arizona.
Letter 9 – Mating Oil Beetles
Subject: Oil Beetle photo
Location: Suffolk, VA
October 26, 2012 9:53 am
I recently took this photo not knowing what they are but they look like oil beetles. Taken in vegetable garden, 10-24-12 in Suffolk, Va. Female was munching on a weed.
Signature: Heidi Pocklington
Letter 10 – Mating Oil Beetles
Subject: Oil Beetles?
Location: Colorado Springs Colorado
July 25, 2014 5:52 pm
Saw these guys while walking the dog today. This was in Colorado Springs, a place I have lived for 25+ years and never seen one of these let alone two “connected” Would love a positive ID.
You are correct that these are mating Oil Beetles, Blister Beetles in the genus Meloe.
Letter 11 – Mating Oil Beetles
Subject: Blue Beetle
Location: Castine Maine
October 11, 2014 10:10 am
Multiple Blue Beetle apparently copulating in path October 5, 2014 in Castine ME. I write a nature column in a local newspaper and wish to include this. I tried three photos before and it would not go. I’ll try one this time.
Letter 12 – Mating Oil Beetles
Subject: Halloween Oil Beetle Orgy
Location: New Haven, CT
November 17, 2015 7:54 pm
This group of oil beetles was having a party in one corner of a lawn in a residential New Haven, Connecticut neighborhood on the morning of October 31. They were all within a one-foot square and there were none anywhere else around.
Thanks to all the hours I’ve spent on your site, I knew exactly what they were! I had never seen any in person before.
The cell phone photos came out pretty well so I thought I’d contribute them for your archives.
You images of mating Oil Beetles from the genus Meloe are a wonderful addition to our archives. It would be curious to know what about the small area where you found them caused the Oil Beetles to congregate so amorously. According to BugGuide: “In males of some species mid-antennal segments are modified, and the c-shaped ‘kinks’ involving antennomeres V–VII are used to grasp female antennae during pre-mating displays.” The individual featured alone in your one image has these modified antennae, hence is a male.
Letter 13 – Mating Oil Beetles
Subject: Identify this bug
October 17, 2016 7:50 pm
I found 2 pair of these bugs while checking my fence line. Michigan, October 16th.
Signature: Brenda Breijak
Letter 14 – Mating Oil Beetles
Subject: Ant/beetle blue and black, has wings and babies attached to it .
Geographic location of the bug: Fredericton, new Brunswick, canada
Time: 07:36 PM EDT
They were all in a patch of grass in a circle ,eating leaves . They have wings but wereel not flying.
How you want your letter signed: Dalton
These are flightless, mating Oil Beetles in the genus Meloe. The larger partner is the female Oil Beetle.