Common species of blue-black spider wasps in North America and around the world include Anoplius atrox, Anoplius americanus, Anoplius lepidus, Anoplius lepidus and Anoplius apiculatus. Blue-black spider wasps are among the most the most difficult insects to identify, as the differences between species, apart from the blue or yellow markings, are generally subtle. The first scientist to classify the genus was Dufour, in 1834.
Blue-back spider wasps have an exoskeleton made of chitin during their adult stage. Their bodies are divided into head, thorax and abdomen, like other members of the of the order Hymenoptera, such as bees and ants. The blue stripes that characterize some species in this genus are often metallic and dark, and can be difficult to observe. Blue-black spiders wasps have two pairs of membranous wings and one pair of antennae, which they use as sensory organs.
Blue-black spider wasps are solitary wasps and use spiders as hosts for feeding their young. The wasps produce a toxin that paralyzes the spider shortly after stinging it. The wasp drags the spider to its nest, sometimes a burrow on the ground, where it lays a single egg on the spider's abdomen. When the larva hatches, it starts to feed on the spider, which is still alive.
Although blue-black spider wasps produce a strong toxin able to paralyze their preys, they are not poisonous to humans, although some people suffer allergic reactions. Blue-black spiders wasps are considered beneficial insects because they help to pollinate crops when feeding on nectar and also regulate the population of some species of venomous spiders that are dangerous to humans.