Harvestmen

Introduction

Harvestmen (Arachnida: Opiliones, Fig. 1) are soft- bodied arachnids that can be found on all continents except Antarctica. There are more than 5,900 species of harvestmen worldwide. Harvestmen can be found in damp, cool places, such as between packs of leaves on the forest floor or in basements and sheds. Harvestmen are rarely seen during the day and become more active at night to feed.

What’s in a Name

Across the globe, people know Opiliones by a variety of names, usually based on their most distinguishing features. In Brazil and Argentina, common names refer to their defensive smell, with names translating to ‘stink bug’, ‘stink spider’, or just ‘bad smell’. Japan and China have names that translate to ‘blind spider’ or ‘blind bug’ because Opiliones sense their environment by waving two of their legs around. Names that relate to the harvest, shepherds, or reapers are abundant across Europe.

This could be due to their presence during the harvesting season, leading to the name ‘harvestmen’. Historically, shepherds would walk on stilts across marshy ground. These long-legged arachnids reminded people of the humans navigating the fields in the same season. In North America, where the most common species are long-legged, the common name is ‘daddy-long-legs’ (Fig. 2).

False Spiders

Opiliones are the third largest group of arachnids after mites and spiders. Although they resemble a child’s interpretation of a true spider, harvestmen are more closely related to scorpions and pseudoscorpions. Harvestmen lack silk glands, their chelicerae (mouthparts) are not adapted to produce venom, and their mouths are tube-shaped, allowing them to ingest whole chunks of food rather than just liquids. Even the number of eyes differs between orders, with spiders famously having eight and harvestmen having between zero and four.

When a spider is threatened, it may bite. This bite may contain venom if the spider feels sufficiently threatened, or it may be a ‘dry’ bite meant to ward off predators. Harvestmen lack this venom. When a harvestman is threatened, it has several ways to dissuade predators. Some species will fake death, called thanatosis, a trait shared with some spiders. Other times, a harvestman will drop a leg that continues twitching as a distraction while it tries to escape (unlike spiders, when a harvestman sheds its skin, it does not regrow lost limbs). A very common defense mechanism involves secreting a noxious smell from its scent glands.

Myths

Across the United States, it’s common to hear that daddy long-legs are the most venomous spider on earth, but their mouths are too small to bite.

Opiliones aren’t venomous and aren’t spiders. Their mouths are large enough to see (Fig. 3). So where did this myth come from? Unlike taxonomic names, common names can be shared across a wide variety of animals. The name ‘daddy-long legs’ applies to both long-legged harvestmen and cellar spiders. To add to the confusion, crane flies are also called ‘daddy-long legs’ in English-speaking countries outside the US. Cellar spiders, in the family Pholcidae, have been found to eat brown recluses, black widows, and red back spiders, all of which are highly venomous to humans. Cellar spiders do not have very high levels of toxicity themselves, but the myth likely began with people watching a spider eat venomous spiders, which then expanded to other creatures with the same common name.

Beneficial Arthropods

Opiliones are not the first arthropods to come to mind when someone considers the term ‘beneficial,’ but they do have their place. Harvestmen feed on soft-bodied insects, preying on aphids, beetle larvae, and caterpillars. They are beneficial not only to suburban gardens but also to larger crops, with studies showing a positive impact on corn and cabbage, where they feed on pest caterpillars. Many opiliones are omnivores that break down detritus and other forms of organic waste that can harbor diseases and fungi.