Family Meloidae - Blister Beetles

Oil Beetles

Meloidae Gyllenhaal, 1810

Family name Meloidae is from genus Meloe Linnaeus, 1758. Origin of that name is not quite clear. The Century Dictionary (1) says etymology is uncertain, as does The Oxford English Dictionary, in its entry for Meloe. It dates first use to 1650, and gives early alternative spellings as Melaones (plural?) and, from a work by Paracelsus (1603) as melloes (genitive case). The OED states this may be related to the name Melolontha, a European scarab called the cockchafer. That genus name is from Greek μηλολονθη, apparently a name for the same scarab beetle.

Other sources derive Meloe directly from a Greek root. The 1913 Webster's Unabridged Dictionary says Meloe is New Latin, from Greek, "to probe a wound". Direct link to an on-line version of the dictionary is here, and here is the text of the entry:

Borror (2) gives an entry for meloe, meloi--Greek meaning "a probe". This root is supported by Woodhouse's English-Greek Lexicon (page 643), which gives "probe a wound" as Greek meloun (μηλουν), quoting use of the word by Aristophanes.

There are 22 genera and approximately 410 Nearctic species (3)

White (4) lists 26 genera and more than 335 species.

Worldwide, approximately 80 genera, 2500 species (Internet searches).

3-30 mm, typically 10-20 mm

Medium to large beetles, typically elongated and rather cylindrical, often found on flowers, foliage. Characteristics:

Blister beetles of eastern U.S. are generally dull in color, but western species are often very colorful (4), apparently aposematic.

Diversity is greatest in arid and semiarid regions, the Southwest (3) (4).

Adult meloids feed on leaves and flowers of several families of plants, particularly Asteraceae, Fabaceae, and Solanaceae (3).

Life cycle is hypermetamorphic. Larvae are parasitoids. Hosts include bees of families Megachilidae and Andrenidae. Epicauta (and other genera) larvae prey on eggs of grasshoppers. Eggs are laid in batches in soil near nests of hosts, sometimes in nest of bee host, or on stems, foliage, or flowers. Larvae undergo hypermetamorphosis--first instar larvae (usually called triungulins) are active, have well-developed legs and antennae. These typically search for hosts. Later instars tend to have reduced legs and be less active, having found hosts. There is a coarctate (pseudopupal) stage, which is usually how the larvae overwinter. Life cycle may be as short as 30 days, or as long as three years. It is typically one year, corresponding to that of host (3) (4) (5).

In some cases, such as genus Meloe, triungulins aggregate and attract male bees with chemical signals (Saul-Gershenz and Millar, 2006).

Pressing, rubbing, or squashing adult blister beetles may cause them to exude their hemolymph (“blood”), which contains cantharidin. This compound causes blistering of the skin, thus the name blister beetle. Accidental or intentional ingestion of these insects can be fatal. There are documented incidents of horses dying after eating hay in which blister beetles were inadvertently baled with the forage. Watch that curious children do not attempt to put these beetles in their mouths. The external use of cantharidin, commercially known as "Spanish fly," the supposed aphrodisiac, is likewise discouraged.

In similar families, head is usually not wider than pronotum (4):