Velvet ant research

Samantha Hall capturing images of velvet ant morphology using the scanning electron microscope (see micrographs below).

We are indebted to Dr. Jim Wetzel at Presbyterian College and Dr. Joan Hudson at Clemson University for their help in our SEM study. The images below were collected with a Hitachi 3400 SEM at Clemson's Electron Microscopy Facility.

 

 

Natural History


Velvet ants are actually solitary wasps, classified into the order Hymenoptera and family Mutillidae. Thus they only superficially resemble ants. Ants and wasps differ in the shape of the region between the thorax and abdomen and the shape of the antenna, the former have a definite bend or elbow in their antenna. There are several hundred species of velvet ants in North America. Most have pronounced hairs (velvet nature) that are often brightly colored in various combinations of red, orange, white, and/or black.


The females are wingless and are capable of inflicting a painful sting and bite if provoked. The bright coloration of velvet ants is probably an advertisement to potential predators of their formidable defenses. The intensity of the sting may be the origins of the common name "cow killer". Although the sting injects venom the dosage and toxicity is quite limited and is not enough to kill a human or a cow.


The adult females are found roaming in environments with sandy soils. They are usually seeking out the ground nests of other bees and wasps, both solitary and colonial species. The female will invade the nest and lay her egg near the host species' egg or larva. When the eggs of the velvet ant hatch, the larva will then feed on the host's brood. They will later pupate and then leave the nest as an adult. The males are winged, lack a stinger, and are known to feed on nectar. It is suggested that females will feed on contents within the nest of their host, either stored food or the larvae.

 

Research Interests


When disturbed, velvet ants will produce a faint but audible sound. The sound is thought to be primarily a warning signal used in defense, which may reinforce the visual signal from the body coloration. Like other species of Hymenoptera, the sound is produced by the rubbing of two abdominal segments together, the edge of one segment acting as a file and the other edge acting as a scraper (see scanning electron micrographs below). This type of sound production is known as stridulation.


Our research is focused on describing the mechanism of how this sound is produced and the conditions that will provoke a response. The file-scraper structure responsible for the stidulation is found in most of the abdominal segments but particular segments may be responsible for producing different elements of the sound. Future studies will focus on the following questions:

1. What is the relationship between the individual abdominal segments and different acoustic components of the stridulation?

2. What conditions will elicit stridulation and what are the benefits of this behavior?

3. How do the acoustic signals and behavior vary among the different species found in the southeast?

 

 


Dasymutilla occidentalis feeding on honey

 

 

Spectrogram of unrestricted stridulation from agitated D. occidentalis. Click on play button below to hear audio recording of above spectrogram.

 

 

File structure of tergite 3

Scraper of tergite 2 (arrows)

 

Scanning electron micrograph of D. occidentalis head region