Desert Blister Beetle: Essential Facts and Tips for Safeguarding

Desert blister beetles are a fascinating species of insects that have gained notoriety among both scientists and nature enthusiasts.

Found in arid regions such as Arizona and Texas, they are known for their distinctive narrow “neck” which contrasts with the broader head and abdomen, giving them an unmistakable appearance.

These beetles can vary in size, ranging from 1/3 to 2/3 inches long.

Blister beetles possess a unique defense mechanism that has captured the attention of both experts and the general public.

When they feel threatened or are held firmly by a person, they can release a yellowish blood from their leg joints, which not only smells bad but can also be dangerous as it contains a substance called cantharidin.

This substance can cause blisters and irritation on human skin if it comes into contact.

Despite their somewhat intimidating reputation, blister beetles are an essential part of the ecosystem. They play a critical role in the control of pests, as they feed on an array of different insects and their eggs.

However, it’s important to be cautious around them and to admire them from a distance, to avoid being exposed to their toxic secretions.

What Do Desert Blister Beetles Look Like?

Desert blister beetles (Lytta magister) are large, brightly colored beetles with orange heads and black backs.

They are over an inch long and have a red head and prothorax, and black elytra.

Blister beetles have soft, oval-shaped bodies, long legs, and narrow necks. They can range in size from 0.39 inches to 0.98 inches.

They can be solid colored (black or gray) or striped (usually orange or yellow and black).

Life Cycle of Desert Blister Beetles

Eggs and Larvae

Desert blister beetles lay their eggs in the soil. After hatching, the larvae are known as triungulins.

They undergo multiple stages, known as instars, before becoming adults:

• First instar larvae are small and mobile
• Later instar larvae are larger and less active

Larvae primarily feed on grasshopper eggs, which provide essential nutrients for their development.

Mating Process

The mating process for desert blister beetles is straightforward:

• Male beetles locate females through chemical cues
• Mating occurs, followed by the female laying eggs in the soil
• Adult beetles die after one reproductive cycle

The Toxic Component: Cantharidin

Effects on Animals and Humans

Cantharidin is a toxic chemical found in desert blister beetles, causing various issues for animals and humans alike:

• Blisters: Cantharidin causes painful blisters and welts upon contact with skin.
• Pain: The toxin induces a burning sensation and can lead to severe pain.
• Swelling: Exposure to cantharidin often results in localized swelling.

In animals, cantharidin poisoning can lead to severe complications.

For example, horses ingesting blister beetles in their hay might experience blistering of internal body tissues and, if left untreated, may eventually die.

Role in the Insect’s Survival

The production of cantharidin serves as a defense mechanism for blister beetles:

• Deters predators: Cantharidin in beetle’s hemolymph can deter many predators, as it is harmful upon consumption.
• Nuptial gift: Males transfer significant amounts of cantharidin to females via a spermatophore during reproduction, providing them protection against predators¹.

In conclusion, cantharidin plays a crucial role in the survival of desert blister beetles by protecting them from potential threats and aiding their reproduction.

Comparison Table: Cantharidin Effects on Humans and Animals

Desert Blister Beetles in Agriculture

Farm Crops and Livestock

Desert blister beetles are pests that can affect a variety of plants and crops, such as alfalfa and flowers.

They feed on leaves, reducing the quality of the plants. In the Sonoran Desert, areas like Arizona and Texas are most affected by these pests.

Alfalfa fields are particularly vulnerable to desert blister beetles’ damage. Horses and livestock are at risk of ingestion, as the beetles may be found in alfalfa hay.

Some dangers this beetle poses to livestock, particularly horses, include:

• Life-threatening inflammations caused by ingesting cantharidin, a toxin present in the beetles
• In severe cases, consumption of as few as 25 to 300 beetles may be lethal to an average-size adult horse

Management Strategies

Farmers and entomologists recommend certain practices to minimize the impact of desert blister beetles on agriculture:

1. Field monitoring: Regular inspections allow for early detection and swift interventions, saving crops from extensive damage.
2. Timely harvesting: Cutting alfalfa before flowering reduces the chances of beetle infestation.
3. Proper field management: Maintaining field borders by removing weeds can help keep beetles from migrating into crop areas.

Here is a comparison table of management strategies:

Through implementing these approaches, farmers can better protect their crops and the well-being of their livestock.

Desert Blister Beetles in Popular Culture

John Alcock’s Big Bad Beetles

John Alcock, a renowned biologist, has written extensively on the topic of blister beetles.

His work, Big Bad Beetles, discusses the life and behavior of these fascinating insects. 

Alcock’s work has helped popularize these beetles and increase awareness about their unique characteristics.

Garden Pests to Marvel at

Desert blister beetles, often considered garden pests, are surprisingly beneficial to certain environments.

While they can wreak havoc on specific vegetables and legumes, they also play a crucial role in controlling other pests.

Even though they pose a threat to certain crops in places like Florida, their dual nature as both pests and beneficial insects makes them a compelling subject for study.

Conclusion

Desert blister beetles, native to arid regions like Arizona and Texas, are renowned for their unique appearance and the toxic cantharidin they contain.

While they play a pivotal role in controlling pests, their toxin can cause blisters and irritation upon contact with human skin.

Their intriguing biology, from their distinctive “neck” to their role in the ecosystem, makes them a subject of both caution and curiosity.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about desert blister beetles. Scroll down to have a look at some of them.

Letter 1 – Arizona Blister Beetle

black-orange bug?
Hello: your web site is really cool. My son and I found a bug outside and we don’t know what it is. We live in Phoenix, Arizona. The bug is pretty big. Maybe 1 inch long. Black body with an orange head.

We found it on a leaf on our Magnolia tree. Just like to know anything about it. Is it harmless? I haven’t seen one of these bugs after living in Arizona for 10 years. So I am curious as to what it is and if it is common around here.
thanks!
Paul Avona

Hi Paul,
You have a photo of an Arizona Blister Beetle, Lytta magister. It is found in deserts in Arizona. Much of the life cycle is still unknown, but adults eat plant tissues of desert shrubs and larvae attacks grasshopper eggs in soil. Blister Beetles secrete a chemical cantharidin which causes blisters on human skin.

Letter 2 – Blister Beetle NOT Checkered Beetle from Arizona

Entomology Student Needs Help!
Bugman,
I’m taking an entomology course at Arizona State University and collected something that has stumped everyone. This beetle was found on a burnt log in the Brown’s Peak Wilderness of the Superstition Mountains, AZ at an altidude of 1933 meters.

Coordinates where found are [ 33°41’41.92″N, 111°19’59.42″W ]. Between two Coleoptera keys, the enormous ASU insect collection/museum, a graduate student and a professor of entomology, we could not key this to the *family* level.

Possibilities we could key to are *Oedemeridae*, *Meloidae*, and *Cleroidea* – however nothing was definite key wise and going by gestalt using the reference collection we could not find anything similar.

For reference, this beetle is 10mm in length. I have attached a couple pictures and have more on my website at: http://corneveaux.com/gallery2/v/Insects/Mystery/ Any ideas? THANKS!!
Jason

Hi Jason,
We like this for one of the Checkered Beetles in the family Cleridae. We will check with Eric Eaton to see if he can verify.

Daniel:
Just checked your site from my workplace. The beetle has ME stumped, too. The habitat and behavior (searching dead wood) really does fit for Cleridae, but the shape of the thing says Meloidae.

It will likely be one of those two. Clerids tend to be very fast-moving, whereas blister beetles mostly polk along. Too bad we don’t know how this one behaved….If I get any more ideas or, um CLARification (pardon the pun), I’ll let you know.
Eric

Ed. Note: (04/23/2007) Eric Eaton just forwarded us these two identifications:
Eric
Great pics. This beast is Tricrania stansburyi, the western species of Tricrania. The species in the eastern US is Tricrania sanguinipennis. Andy Cline, CA Dept. Ag. and myself are doing a revision of this genus.
Jeffrey P. Huether

That’s a bee-parasitic Meloid, Tricrania. Not very common.
Doug Yanega
Dept. of Entomology: Entomology Research Museum
Univ. of California – Riverside,
Riverside, CA