Blister Beetles

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Have you heard about Blister beetles yet? Belonging to the Meloidae family, blister beetles are known for their secretion of the highly toxic chemical agent Cantharidin. Primarily used by the insects for defensive purposes, cantharidin is known as a vesicant compound, which causes severe water blisters and irritation on the skin, eyes, and gastrointestinal tract.
Blister Beetles

About 7,500 species of the Blister beetle have been reported globally to date, with a large number of sub-families and other associated insects within the Meloidae family. They are regarded as parasites, and aren’t something you would want in your farm.

Appearance: What do they look like?

The blister beetles often have a bright, shining, often metallic appearance, making them easy to notice in the natural environment, similar to Spanish Fly. Most beetles are conspicuously colored and are found in nature to be displaying aposematism, warning potential predators that they are highly toxic and not worthwhile eating.

They range between 3 to 20 mm in length (0.1 to 0.8 inches). The majority of them are between 10 to 15 mm (0.4 to 0.6 inches). They possess long, slim rugged bodies that are often covered with blue or green wings. Markings such as bands and/or stripes are common among the blister beetles.

What is their Life Cycle?

Blister Beetles

Hypermetamorphosis is common among blister beetles. They undergo several changes during their lifespan from birth to adulthood. The initial stage is the larval stage, which occurs right after hatching from their egg. During the time they are larvae, blister beetles climb up flower stems and wait for the arrival of a bee.

This first stage is one of mobility, and the larvae are known as triungulin. They attach themselves to the body of the bee. And if the bee happens to be a male, they wait to further transfer themselves on the body of a female bee.

Upon arriving in the hive, the insectivorous larvae destroy all the bee’s larvae, eating the eggs of the female bee along with other food materials she was saving. Once they attain adulthood, they leave the hive and feed on the leaves of plants such as Amaranthaceae, Asteraceae, Fabaceae, and Solanaceae.

The behaviour at the larvae stage can be termed as parasitic and predatory. The cycle is repeated after mating.

The male blister beetle transfers some of the cantharidin that it secretes to the female during the mating ritual, along with the spermatozoa. The highly blistering cantharidin is mainly used to protect the eggs from external predatory attacks.

The blister beetles are found throughout most parts of Europe, with reported sightings in North America too. The associated oil beetle is known to belong in the Meloinae family and is much shorter in size and stature. The different body structure also includes a forceps-like antenna, which is used to hold the female during mating. Here is a short detail of the related subspecies of the blister beetles.

Cantharidin

In the case of human beings, cantharidin poisoning generally occurs from external administration. Cantharidin has been historically used as an aphrodisiac and sexual stimulant. It is a potent vesicant (blistering agent), exposure to which can cause chemical burns.

Notable Genus among the Blister Beetles

The Blister beetles are divided into several subgroups. Here is a look at them below.

  1. Genus Cerocoma: Found across the entire Mediterranean region and the northern part of Africa, this Palearctic genus of blister beetle has 9 segmented antennae. It has evolved into a strong sucking tube. The adults feed on Asteraceae and Apiaceae plants. They have well-developed wings and long, slender legs. There are about 27 species, including the Cerocoma festiva.
  2. Genus DiaphoroceraI: Found in the Sahara-Sindh regions of Palestine, Israel, North Africa, southern Iran, and the Arabian Peninsula, members of this genus have a metallic-green blue body, modified antennae, and orange-yellow legs. This genus contains about 10 species.
  3. Genus Epicauta: Epicauta is available throughout all corners of the world except Australia. They are particularly diverse throughout the Arizona region of the USA. A few species are found near the Arctic in the Northwest Territory of Canada. The larvae feed on grasshopper eggs, and the adults feed on leaves from crop fields. Known globally as a pest, Epicauta is a huge blister beetle genera, with more than 300 described species.
  4. Genus Tegrodera: Known as the iron cross soldier beetles, there are at least 3 described species. The Tegrodera aloga is primarily found in Central America and North America. Easily identifiable due to bright yellow-red markings/spots on the body, the iron cross blister beetle feeds on the flowers of sand bells, rough nama, and woolly stars.
  5. Genus Berberomeloe: Part of the Lyttini tribe, the Genus Berberomeloe beetles are also known as oil or blister beetles. They belong to the family Meloidae and are unique among the blister beetles. They have a number of unique features that are not found among any other beetles, including the reduced elytra (forewing), no wings, and modified antennae. The entire genus is endemic to the Western Mediterranean region, spreading throughout the Iberian Peninsula, France, Algeria, Morocco, and Tunisia. There are 2 known species. The Berberomeloe majalis is further found only in the Spanish region of Granada Almeria and Murcia.
  6. Genus Lytta: The Genus Lytta contains many important members of the blister beetle category, including arguably the most famous Spanish Fly (Lytta vesicatoria). There are about 100 species in this genus, with about 70 of them native to North America.
  7. Genus Muzimes: Belonging to the family Meloidae, the Muzimes is found in the European regions of Bulgaria, Greece, Malta, Macedonia, Moldova, Romania, and Southern Russia. There are 5 species in this genera, with the Muzimes Collaris being one of the largest blister beetles, growing up to 46-50 mm (around 1.6 to 2inches) in length.
  8. Genus Zonitis: It is one of the largest genera of blister beetles found throughout the world. First named and described by Johan Cristian Fabricius in 1775, there are more than 100 species in all different colors and sizes. Notable species in this genus include the Zonitis fogoensis (endemic to Fogo Island, Cape Verde), and Zonitis Vittigera (Found in North America).
  9. Genus Hycleus: Found primarily in Africa, Asia, and India, the Hycleus is often confused with the Mylabris genus. The adult feeds on a wide range of flowers and can be a problem if present in large numbers, as they tend to destroy flowers of leguminous crops.

Have you come across any of these? They are as intriguing as they are dangerous.

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