Daddy Longlegs: Arachnids, but Not Spiders

Daddy longlegs

 pachytime / Flickr / CC BY-ND 2.0

People often mistake a daddy longlegs, also called a harvestman, for a spider. Daddy longlegs do have some spider-like qualities since, like spiders, they are classified as arachnids. Like all arachnids, they do have eight legs and tend to skitter about the way spiders do. We often see them in the same places where we see spiders. In fact, daddy longlegs are more like scorpions than spiders.

Arachnids

Other critters that are arachnids include scorpions, mites, and ticks, and those arthropods are certainly not spiders. In fact, arachnids are not insects either. Insects are animals with six legs, wings, or antennae. Arachnids have none of the above.

Opiliones Compared to Araneae

The daddy longlegs belongs to the order OpilionesUnlike in spiders, the number of eyes of daddy longlegs, as well as body type, sex organs, and defensive mechanisms, are all different. In opilionids, the head, thorax, and abdomen are fused into one thoracic cavity. Spiders, of the order Araneae, have a distinct waist between the cephalothorax and the abdomen. Opilionids have just two eyes, compared to the usual eight in spiders.

Daddy longlegs also do not produce silk, unlike spiders. They do not spin webs, and they do not use webs to capture prey. If you find a harvestman in a web, it does not live there. It probably would like to be rescued from the spider that is about to eat it.

Finally, daddy longlegs are not venomous. They do not have fangs, nor venom glands. Most spiders, with only a few exceptions, produce venom.

Special Adaptations

Daddy longlegs stink when threatened, thanks to defensive stink glands, which have been observed to repulse predators. Daddy longlegs are usually extremely well camouflaged. During the day, many of them hide in crevasses, and when disturbed, they usually curl up and remain motionless for several minutes by playing dead—which works extraordinarily well.

Anyone who has tried to catch a daddy longlegs knows they have a tendency to shed their legs. Grab one by the foot, and it promptly lets go of the entire leg and runs off. They will voluntarily shed legs to get away from predators, but sadly a new appendage does not grow back if it is already full grown. There is some hope if it is in the nymph stage that the leg might grow back.

Its legs are not just vital to locomotion, they are also nerve centers. Through its legs, the daddy longlegs may sense vibrations, smells, and tastes. Pull the legs off a harvestman, and you might be limiting its ability to make sense of the world.

Mating Behavior and Sex Organs

Unlike spiders that use an indirect method of transferring sperm to females, the harvestman does tend to have elaborate mating rituals and a specialized organ capable of depositing sperm directly into the female. In some harvestman species, there are "sneaky males" also known as beta males, who camouflage themselves as females, get close to a female and plant its seed into unwitting females.