Rain beetles, belonging to the family Pleocomidae, are fascinating insects that tend to emerge during rainy seasons. These insects are generally harmless and not known to bite humans, making them interesting subjects for observation.
As rain beetles stay mostly underground and are rarely encountered, their adult stage is marked by intriguing activity. After surfacing, male beetles are capable of flight, while wingless females reenter their burrows, as mentioned on WSU Tree Fruit. When discussing rain beetles, it’s important to note their mild nature and unique habits.
Adding to their mystery, rain beetles often remain hidden and are classified into different species based on their field appearances during August and September. Despite not being a significant threat to humans or plants, studying these insects can broaden our understanding of the insect world and contribute to appreciating the diversity of nature.
Rain Beetles Overview
Defining Characteristics
Rain beetles, belonging to the genus Pleocoma and family Pleocomidae, are fascinating insects. They have some unique features:
- Large, robust, and shiny
- Hairy: Pleocoma means abundant hair in Greek1
These beetles spend most of their lives underground as larvae, feeding on tree roots, fungi, and other organic matter1.
Geographical Distribution
Rain beetles are found primarily in North America, specifically in the western United States2. Different species of rain beetles emerge at varying times in the field2. These insects have notable characteristics concerning their emergence and behavior:
- Pupae transform to adults in August and September2
- Adults can live for months but do not feed2
- Only male beetles can fly2
Comparison Table
| Feature | Rain Beetles | Other Beetles |
|---|---|---|
| Diet (as larvae) | Tree roots, fungi, organic matter1 | Varies by species |
| Flight | Only males can fly2 | Typically both sexes |
| Hairiness | Abundant hair1 | Not a common feature |
Rain Beetles Behavior and Life Cycle
Rain beetles are found only in western North America, particularly in fruit-growing areas of the Pacific Northwest1. These beetles are known for their unique behaviors, such as flying during the rain and possessing flightless females.
The life cycle of rain beetles consists of four stages: egg, larva, pupa, and adult1. Females lay eggs in the soil, after which they develop into larvae.
Larvae primarily feed on tree roots1. They burrow in the soil, consuming roots throughout their larval stage. This stage plays a significant role in their development and growth.
Once fully grown, rain beetle larvae pupate in soil chambers1. Pupation marks the transition from larva to adult, during which they undergo significant physiological changes.
Adult rain beetles are typically flightless (females) or fly during rainfall (males)1. These beetles use their antennae to detect pheromones emitted by females, guiding them to potential mates.
Here’s a brief comparison table:
| Rain Beetle Stage | Main Characteristics |
|---|---|
| Egg | Laid in soil by females, initiates life cycle |
| Larva | Feeds on tree roots, burrows in soil |
| Pupa | Transforms from larva to adult in soil chambers |
| Adult | Flightless females; males fly during rain |
Some key features of rain beetles include:
- Flightless females
- Males that fly during rain
- Larvae that consume tree roots
- Burrow in soil throughout life cycle
When observing rain beetles, keep the following characteristics in mind:
- Males use antennae to detect female pheromones
- Follow a complete metamorphosis life cycle
- Found in western North America
- Primarily inhabit mountain habitats
While rain beetles possess strong mandibles, they are not known to bite humans. Their focus is mainly on their life cycle, involving laying eggs, feeding on tree roots, developing in soil chambers, and engaging in mating rituals related to rain.
Do Rain Beetles Bite
Rain beetles are known for living underground and feeding on shrub and tree roots, fungi, and other organic matter. They do not typically pose a threat to humans, as their primary focus is to find food and reproduce.
However, if you happen to encounter one of these beetles, it’s important to exercise caution. Some beetle species might bite if provoked or threatened. Let’s explore some related beetles and their potential to bite:
Examples of Beetles:
- Stag Beetles
- Bark Beetles
| Beetle Type | Bite Probability | Pain Level | Harmful to Humans |
|---|---|---|---|
| Rain Beetles | Low | N/A | No |
| Stag Beetles | Medium | Low | No |
| Bark Beetles | Low | N/A | No |
Characteristics:
- Strong jaws
- Sharp teeth
- Different diet and prey preferences
In the case of the rain beetle, their jaws are not designed for biting humans. Whereas stag beetles have powerful jaws, they use them to fight other males during mating season and tend to avoid humans.
In summary, rain beetles are unlikely to bite. The risk of being bitten by other related beetles is usually minimal when handled gently.
Environment and Habitat
Rain beetles, belonging to the genus Pleocoma, are found predominantly in western North America, particularly in the Pacific Northwest1. These beetles thrive in environments with abundant organic matter, such as shrubs and fungi, which provide them energy for growth and reproduction2.
The rainfall plays a key role in the life cycle of rain beetles. Adult beetles emerge from the ground and become active during periods of heavy rain3. Additionally, rain provides the moisture needed for the fungi and other organic matter that supports their habitat4.
Some rain beetles have been found in fruit-growing areas, such as apple orchards5. These environments offer a combination of factors that benefit the beetles, including:
- Sufficient organic matter
- Availability of fungi
- Shaded areas provided by shrubs and trees
Despite their presence in fruit-growing areas, there is no evidence to suggest that rain beetles pose any threat to humans or that they bite. So, you can enjoy these beetles in their natural habitat without any concern for your safety6.
Rain Beetles and Humans
Rain beetles are unusual insects that live underground for most of their lives. They emerge only under specific conditions, such as heavy rainfall. Despite being a curious and fascinating species, rain beetles don’t have a significant impact on humans.
As underground larvae, rain beetles feed on shrub and tree roots. In some cases, they can become pests, particularly if they attack the roots of fruit trees, such as apples or pears1. However, these beetles are not known to bite humans, and they are generally considered to be harmless.
Some characteristics of rain beetles include:
When it comes to controlling rain beetles, insecticides might not be the best option. Since they spend most of their lives underground, insecticides may not reach them effectively. Instead, proper care and maintenance of fruit trees can help minimize potential damage.
It’s also worth noting that although rain beetles have abundant hair, they are not known to cause allergic reactions in humans1. Additionally, these beetles are not attracted to artificial lights, unlike some other insect species.
In summary, rain beetles are fascinating insects that live mostly out of sight. While they can sometimes be pests for certain fruit trees, they are harmless to humans and don’t pose allergy risks.
Interesting Facts and Insights
Rain beetles are a fascinating group of beetles found mostly in the western North American regions such as Washington, California, and Oregon1. They are closely related to scarab beetles and have some unique characteristics, including:
- V-shaped scoop
- Spiral pattern
- Abundant hair
Rain beetles have a V-shaped scoop on their heads that helps them to dig through the soil2. Their bodies exhibit a spiral pattern, which is a striking feature they share with scarabs3. These beetles also have abundant hair, giving them a distinctive appearance4.
These beetles are known as “Pleocoma sp.”5 and are often seen in December, particularly the male rain beetles6. They have a fascinating life history, involving several stages:
- Nymph
- Algae
- Grubs
The nymphs of rain beetles are usually found near bodies of water, where they feed on algae7. As grubs, these critters primarily feed on roots, fungi, and other organic matter8.
Rain beetles are known to lay their eggs near trees9 and can sometimes be a pest to fruit trees, such as apple and pear trees10. These beetles share some common habitats with mosquitoes, crabs, and other insects11.
Here’s a comparison table highlighting key differences between rain beetles and scarab beetles:
| Rain Beetles | Scarab Beetles |
|---|---|
| V-shaped scoop on head | No V-shaped scoop |
| Spiral pattern on body | No spiral pattern |
| Abundant hair | Less hairy |
| Found in wet environments | Found in diverse habitats |
| Primarily in western North America | Widespread distribution |
As mentioned, rain beetles can sometimes be problematic for fruit trees. However, they also play a crucial role in the ecosystem as a food source for other animals and by helping to recycle nutrients in the environment.
Footnotes
- (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19974) ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8 ↩9 ↩10 ↩11 ↩12 ↩13 ↩14
- (https://treefruit.wsu.edu/crop-protection/opm/rain-beetles/) ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8 ↩9
- https://extension.umn.edu/nuisance-insects/ground-beetles ↩ ↩2
- https://hort.extension.wisc.edu/articles/beetles/ ↩ ↩2
- https://treefruit.wsu.edu/crop-protection/opm/rain-beetles/ ↩ ↩2
- https://extension.umn.edu/nuisance-insects/ground-beetles ↩ ↩2
- https://entomology.si.edu/resources/faq/geninfo/type_houseinsects.html ↩
- https://bugguide.net/node/view/15497/bgpage ↩
- https://entomologytoday.org/2017/12/04/rain-beetles-emerge-chasing-the-nasty-weather/ ↩
- https://extension.umd.edu/hgic/topics/apple-pear-wood-boring-beetles ↩
- https://www.aphis.usda.gov/aphis/resources/pests-diseases/hungry-pests/the-threat/environment+ ↩
18 Comments. Leave new
I was searching for information on a beetle that we have had at our house in the winter in Twain Harte, CA. The bugs are very attracted to light and are found at the front of the house and in the garage. They fly around but seem to die quickly (in days). We have up to 10+ at a time. From what I have read, the beetles are a Rain Beetle. I have read that the flying beetles are male and live 10-12 years, but with the amount of dead beetles that we have, 10-12 years seems a long time. Can anyone give me some more information on these beetles? Does the freezing cold kill them?
The 10-12 year lifespan is spent in the larval stage underground. Adult Rain Beetles live a very short time and do not feed. There are some species that fly in near freezing weather. We have loads of information on Rain Beetles on our website and we would recommend using the search engine to locate this information and the links to outside sources.
What an awesome story that they were named after your mentor! They remind me of our June Bugs which are pretty awesome.
They are glorious little beings and I love the fancy antennae and furry leggings.
You may read a great article on Rain Beetles from the LA Times several years back.
This is a unique specimen and does not represent anything described by locality , if your location information is correct . You have something new recorded for that area ! 1. We have over a dozen Unidentified Pleocoma in the central valley that need to be named and this is either one of these…….. or…. 2. something …. different . 3….only Pleocoma crinita or Pleocoma conjungens comes close in appearance with current described Species . So , it looks like I will have to spend some time looking for these ” Auburn ” specials . Let me know if you get any more for a Exact physical description . Very nice ! Gene St. Denis SNR
Hi Gene,
What’s That Bug? is very grateful for all of the information you have provided over the years regarding Rain Beetles. We hope you will continue to update us to your findings.
Daniel and Mark , after examining your Pleocoma photos I believe that you have dead male Pleocoma puncticollis or male Pleocoma australis . Mark , ( if you read this at such a late response date ) I would like some specimen examples if possible in the future or Better Yet Photos (of head and antennae in particular ) . Cheers Gentlemen ! Gene St. Denis Sierra Nevada Research P. S. I am sitting at a ‘Warm ” home in South Lake Tahoe @ 6,500 feet with a Large Mug of steaming Hot fresh French Roast Coffee , going thru Pleocoma records on the “Computer ” with a white out Blizzard ragging outside .
Thanks Gene. We are expecting several inches of rain here in the Los Angeles Basin today.
Daniel and hollyazevedo , if possible I would like to see some Good pictures of the Elytra and Head if possible to verify . If what Frank said is true and these match the series that I have Collected last year and last week…. then it is the ” undiscribed ” species. It is a shame that Frank didn’t get the time to Finnish it and others he was working on . It could be the illusive ” Red Staff ” or ” Pleocoma iridescenta ” , which are the nick names of a undiscribed species ! Cheers! Gene St. Denis Sierra Nevada Research
Glad to see one named after Frank. Was too trained by Frank and knew him for 33 years. Sure do miss him. Was at the BioQuip open house yesterday and noticed an unidentified Pleocoma from Tehama County … am guessing that was Hovorei? May have to get one next time I am over there.
So if I found one does it mean there is a partner near by?? It was in the house by the be. Will they get on humans?? Traumatized.
Pleocoma season is approaching and I hope Gene St. Denis will be out there pursuing his obsession again.
He is certainly passionate about these creatures.
I have only seen rain beetles once. Near Simi, Ca, in the hills. It was February and raining buckets. Me and a couple other boys decided to go look for them.
We found some! The beetles are awesome, seldom seen and so interesting.
But I think the most fun was being out there in such a storm, when everybody else was hunkering down, and actually finding a creature we were pretty sure doesn’t exist. It opens the mind.
Pleocoma season is approaching and I hope Gene St. Denis will be out there pursuing his obsession again.
He is certainly passionate about these creatures.
I have only seen rain beetles once. Near Simi, Ca, in the hills. It was February and raining buckets. Me and a couple other boys decided to go look for them.
We found some! The beetles are awesome, seldom seen and so interesting.
But I think the most fun was being out there in such a storm, when everybody else was hunkering down, and actually finding a creature we were pretty sure doesn’t exist. It opens the mind.
I believe that you had an early flight of Pleocoma hoppingi males . And of coarse a Male Pleocoma hoppingi . Cheers ! Gene St.Denis Sierra Nevada Research
Thanks Gene.
Folks , I now have some ideas about it being a male Pleocoma fimbriata ( northern sub group ) . With a head lam shoot I could pin it down . Cheers ! Geno
My daughter and her Aunt found what looks to be a male rain beetle in Cherryvale Kansas. We have had some severe flooding lately.
The range of Rain Beetles is limited to the west coast.