Known for their velvety integument, velvet worms are considered to be close relatives of the Arthropoda — insects, spiders, crabs, etc. They belong to a small phylum of elongated, soft-bodied, worm-like animals that possess numerous walking legs.
Approximately 200 species have been described, although the number of species is likely much higher. They range in size from 0.2 to 8 inches in length and have between 13 and 43 pairs of unstructured body appendages or legs used for walking. They live in all tropical habitats and in the temperate zone of the Southern Hemisphere.
The sexes are separate and the females are usually larger than the males. The transfer of the male sperm varies in different species. For example, some males have a small pit on their head and the male will transfer sperm to this pit which then makes contact with the female's genitalia.
There is an African species where the male leaves a packet of sperm on the body of the female. The packet dissolves and the sperm are absorbed through the skin. Inside the body the sperm swim to the ovary where fertilization takes place. The females of some species lay fertilized eggs, while in other species the young are born alive.
They usually hunt only at night, feeding on almost any small invertebrates such as lice, crickets, cockroaches, millipeds, etc. On the third head segment to the right and left of the mouth, are two nozzle-like extensions with openings called “oral papillae.” Each one is the opening for a large internal highly branched slime gland, which produces large quantities of a milky-white slime. This slime can be aimed and expelled simultaneously from the two papillae as streams of adhesive liquid traveling at a speed of 10 to 20 feet per second.
The slime is high in protein, which gives it high tensile strength and stretchiness for use in ensnaring prey or for defensive purposes. It is a very effective weapon when hunting or defending itself.
After ejection, the slime dries quickly. In the process it shrinks a great deal, loses its stickiness, and becomes very brittle. Once the slime hits the target, it's over very fast for the recipient. The movement of the struggling target, such as an insect, creates a netlike trap that quickly immobilizes the unlucky target.
Larrie Stone is a retired Dana College science professor.