Wild Facts About The Red And Black Blister Beetle
Meet The Red And Black Blister Beetle
- Blister Beetles may look like your average garden insect, but their strange life cycle, eye-catching colors, and chemical defenses make them one of the most fascinating beetles around.
- Found across the eastern United States, these beetles are full of surprises—from their love lives to how they protect themselves from predators.
What Do Blister Beetles Look Like?
- Adult Blister Beetles are long, soft-bodied insects that have:
- Broad heads,
- Downward-pointing mouthparts that help them chew plant leaves.
- Abdomens with 11 segments,
- Soft, leathery wing covers that curve around the sides of their abdomens but don’t cover the tips of their abdomens.
- Many blister beetles fly while some species, like Tricrania sanguipennis, can’t fly at all.
- These beetles crawl along the ground and are common in sandy areas where solitary bees nest.
What Do Blister Beetles Eat?
Adult Red And Black Blister Beetles
- Mature Red and Black Blister Beetles are herbivores.
- They love leaves and flowers, especially from plant families like Asteraceae, Fabaceae, and Solanaceae.
- Blister Beetles are usually active during the daytime, with their numbers peaking in mid-summer, especially July and early August.
- In large numbers, they can become pests, damaging crops like alfalfa, beets, potatoes, and tomatoes.
Red And Black Blister Beetles Larvae
- Red and Black Blister Beetle larvae feed on grasshopper eggs or nectar and pollen from solitary bee nests.
- Blister beetle larvae eat large numbers of grasshopper eggs—especially from the common Differential Grasshopper (Melanoplus differentialis)—so they help reduce damaging grasshopper populations in gardens and fields.
- Populations of blister beetles often rise the year after boom in the grasshopper population, thanks to plentiful supplies of grasshopper eggs for the blister beetle larvae.
Strange Courtship: Antenna Pulling
- Blister Beetle romance starts in a unique way.
- Males use a behavior called “antenna pulling” to attract a mate.
- The male approaches the female from behind and gently tugs on one of her antennae with his legs.
- It’s a subtle but important part of their courtship ritual (Evans 2014).
A Bizarre Babyhood: Hypermetamorphosis
- Most insects grow through a series of similar-looking stages called instars, getting bigger each time they shed their skin.
- Blister Beetles, however, go through something much more unusual: hypermetamorphosis.
- During hypermetamorphosis, the larvae change shape dramatically as they grow.
- The first stage is called a triungulin—a tiny, active, and mobile larva with long legs.
- Triungulins crawl around in search of a host, like underground grasshopper eggs or bee nests.
- Once they find hosts, they molt into a slower, legless form that stays put and starts feeding.
- After this, they change again into a grub with small legs that helps them prepare for the next stage—pupation (Evans 2014).
Defense: Bright Colors and Blistering Chemicals
- Blister Beetles aren’t fast, but they have powerful defenses.
- Some species, such as the Red and Black Blister Beetle, have brightly colored bodies that signal a warning to potential predators that the beetles aren’t safe to eat.
- This warning coloration is called “aposematic coloration”.
- Red and Black Blister Beetles back up the warning sent by their bold red and black coloration with a serious chemical defense.
- These beetles contain cantharidin, a toxic chemical that causes severe blisters on skin and in mouths.
- When threatened, the beetles ooze cantharidin-rich fluid from their leg joints—a defense shared by many other beetles, such as Ladybugs and Big Dipper Fireflies (Photinus pyralis).
- Cantharidin makes blister beetles taste terrible and deters many predators, such as Common Raccoons (Procyon Lotor) (Carrel 1999, https://doi.org/10.1023/A:1020970624529).
- Interestingly, other blister beetles, such as the Bronze Blister Beetle (Lytta aenea) have very drab coloration despite also using cantharidin in their own defense.
- But not all predators stay away. Some animals, including both birds and other insects still attack them. These include:
- Robber Flies (family Asilidae),
- Mantids like the Chinese Mantis (Tenodera sinensis) and the Carolina Mantis (Stagmomantis carolina),
- Eastern Meadowlarks (Sturnella magna),
- Eastern Bluebirds (Sialia sialis),
- Southern House Spiders (Kukucania hibernalis) (Carrel 1999, https://doi.org/10.1023/A:1020970624529)
- Some Blister Beetle species are even cannibalistic—their larvae may eat their siblings.
- Others, like the Red-Headed Blister Beetle (Epicauta atrata), prey on the eggs of other Blister Beetle species, such as the Striped Blister Beetle (Epicauta vittata).
Cantharidin: Potent and Persistent
- Cantharidin is incredibly strong.
- Even small amounts can burn or blister skin and damage internal tissues. This makes Blister Beetles dangerous not only to predators but also to livestock.
- A common species, the Black Blister Beetle (Epicauta pensylvanica), often swarms hay plants like alfalfa.
- When these beetles get baled into hay and eaten by animals, the results can be deadly—especially for horses.
- Just 1 mg of cantharidin per kg of body weight can kill a horse. Symptoms of poisoning include blisters, colic, fever, rapid heart rate, sweating, diarrhea, and even death (Williams 2009).
- Even more toxic is the Striped Blister Beetle (Epicauta vittata), which carries five times more cantharidin than the Black Blister Beetle (Williams 2009).
- Worse still, cantharidin doesn’t go away after the beetles die.
- It remains active in dried beetles and contaminated hay, posing a serious threat to animals long after the insects are gone.
- Cantharidin concentrations vary by sex in at least one Blister Beetle species, the Bronze Blister Beetle (Lytta polita).
- A study that researched the responses of Common Raccoons and Southern House Spiders to Blister Beetles as prey found that “the concentration of cantharidin in L. polita males (about 1.1% of dry weight) was about five times higher than that detected in females (about 0.2% of dry body mass) (Carrel 1999, https://doi.org/10.1023/A:1020970624529).
Nature’s Thieves: Beetles That Steal Defense
- Blister Beetles aren’t the only insects that use cantharidin.
- Some beetles from the Anthicidae family, also known as Antlike Flower Beetles, scavenge dead Blister Beetles to collect cantharidin for themselves.
- Males even pass it to females during mating.
- The females then use the chemical to protect their eggs and larvae (Evans 2014).
Scientific Classification
|
Kingdom |
Animalia (animals) |
|
Phylum |
Arthropoda (arthropods) |
|
Class |
Insecta (insects) |
|
Order |
Coleoptera (beetles) |
|
Family |
Meloidae (blister beetles) |
|
Genus |
Tricrania |
|
Species |
T. sanguipennis |
Scientific Name |
Tricrania sanguipennis |
Red And Black Blister Beetle Photo Gallery
Blister Beetle. Tricrania sanguinipennis. Insect. Photograph taken and design created by the author. Copyright © 2025 Now I Wonder. All rights reserved.- Blister Beetle. Tricrania sanguinipennis. Insect. Photograph taken and design created by the author. Copyright © 2025 Now I Wonder. All rights reserved.
- Blister Beetle with key for scale. Tricrania sanguinipennis. Insect. Photograph taken and design created by the author. Copyright © 2025 Now I Wonder. All rights reserved.
- Blister Beetle. Tricrania sanguinipennis. Insect. Photograph taken and design created by the author. Copyright © 2025 Now I Wonder. All rights reserved.
- Blister Beetle with key for scale. Tricrania sanguinipennis. Insect. Photograph taken and design created by the author. Copyright © 2025 Now I Wonder. All rights reserved.
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