January 2010 Archives

Velvet ants are wasps that sometimes look like ants.  Velvet ants are often covered with hairs giving them a velvet-like appearance. They are usually black or brown, but sometimes they can have eye-catching coloration such as red, yellow or orange. Sizes can can range from 6-30 mm (0.25-1.5 in.). Both velvet ants and true ants are in the order Hymenoptera, (which also includes bees and other wasps), but velvet ants are in their own family, the Mutillidae, whereas all true ants belong to the family Formicidae. 

In temperate regions, velvet ants (hereafter, mutillids) are usually easy to tell apart from true ants because they are so hairy.  Although some tropical ants can be quite hairy, like this Echinopla from Borneo, this Calomyrmex and this Polyrhachis, both from Australia, very few ants are as large and hairy as mutillids.  Another important difference between ants and mutillids is that ants usually have a very long first antennal segment, followed by 3-12 very short segments (picture).  This antennal morphology is called "elbowed," or "geniculate." Mutillids do have a slightly elongate first antennal segment, but it never extends much beyond their face. 

There are approximately 6000 species in the Mutillidae. Female mutillids are wingless and have an ant-like appearance, whereas males have wings. They often produce sound by rubbing body parts together, or stridulation. They have a very painful sting, which is why they are sometimes referred to as "cow-killers". The sting is usually more painful than a bee sting. However, as velvet ants are solitary insects, the attack of multiple individuals is rare.  

Mutillid ecology

Little is known about mutillid ecology. From the species that have been studied, we know that they are often parasites of ground-nesting bees and wasps, like bumble bees. Mutillid larvae are usually external parasitoids of their host species. This means that the female mutillid wasp lays an egg close to a pupa and does not place it inside the pupa. A review on mutillids as parasites of social insects is given by Brothers et al. (2000). According to "Brothers' rule" (Brothers 2000), "larvae of the mutillid wasps are always ectoparasites of host stages which are enclosed in some sort of package (cell, cocoon, puparium, ootheca) and which are not actively feeding". Most commonly, host species are from the groups of wasps, bees (Hymenoptera), flies (Diptera), beetles (Coleoptera) (Brothers et al. 2000 and references therein).

Some mutillid wasps mimic ants. One species, Pappognatha myrmiciformis, mimics the ant Camponotus sericeiventris as described by Wheeler (1983). The purpose of this mimicry is not clear. As mutillids possess a very painful sting and have a very hard exoskeleton, this mimicry probably does not serve a protective function. Wheeler (1983) hypothesizes that the resemblance might enable females to enter the nest of C. sericeiventris and parasitize the brood. However, Brothers et al. (2000) find it more likely that the larvae of the parasitoid feed on myrmecophilic (ant loving) beetles that live within the ant colonies.

Brothers DJ, Tschuch G, and Burger F  (2000)  Associations of mutillid wasps (Hymenoptera, Mutillidae) with eusocial insects. Insect. Soc. 47: 201-211.

Wheeler GC (1983)  A mutillid mimic of an ant (Hymenoptera: Mitillidae and Formicidae).  Entomol. News 94: 143-144.

Dasymutilla gloriosa.jpg

Dasymutilla gloriosa - Thistledown Velvet Ant. California, USA. Photo by Alex Wild (www.alexanderwild.com)

Sphaeropthalma arota.jpg

Sphaeropthalma arota - nocturnal velvet ant. California, USA. Photo by Alex Wild (www.alexanderwild.com)

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