Harvestmen, otherwise known as daddy long-legs (not to be confused with the cellar spiders of family Pholcidae, which are also described as daddy long-legs) bear a striking resemblance to spiders, but they actually belong to a separate order of arachnids known as Opiliones. These strange-looking creatures have eight legs, but only two eyes, and their body segments are largely fused together, giving the body a noticeably rounded, pill-like appearance.

Above: Metagryne bicolumnata, commonly known as the bunny harvestman

There are roughly 6,700 known species of harvestman, but researchers estimate that a total of more than 10,000 species may currently exist. Their physical features vary greatly from one species to the next; some harvestmen have crab-like claws, spikes, thorny legs, elongated bodies, colorful features, or cryptic markings. Most of them are equipped with long, spindly legs, but there are some that have shorter, stockier limbs instead.

Above: Megabunus diadema and two unidentified species from family Sclerosomatidae

Unlike spiders, harvestmen have an omnivorous diet that includes fungi, fruit pulp, seeds, pollen, lichen, algae, and invertebrate prey, and they are capable of consuming solid food, whereas spiders are typically carnivorous and feed only on fluids.

Above: a harvestman from genus Chasenella munching on a mushroom-cap

As this article explains:

Harvestmen consume mushrooms, fruit pulp, seeds, and seed appendages more frequently than spiders probably because they are “solid food feeders," which means they can ingest solid tissues by biting off small pieces. In turn, spiders are “fluid feeders” and feed on vegetable matter most frequently in the form of fluids (e.g. nectar, stigmatic exudate, plant sap, and honey dew) rather than fungal or plant tissues.

Above: genus Marthana

When given a choice between fresh fruit or invertebrate prey, some harvestmen actually prefer the fruit:

Schaus et al. carried out a feeding trial in which the Neotropical harvestman Erginulus clavotibialis was given a choice between fresh pineapple and live invertebrate prey. This harvestman demonstrated a distinct preference for fruit over the invertebrate prey.

Above: Dentobunus quadridentatus

Harvestmen are also much more social than spiders, and the males of some species have been known to engage in paternal care, which is a trait that rarely occurs among arthropods:

Single fatherhood is the rarest form of parental care in nature. Still, males are often the sole caretakers of progeny among a number of species of daddy long-legs, also known as harvestmen. In these species, fathers are exclusively responsible for guarding eggs that females lay on the undersides of leaves; the males remain on the eggs nearly constantly for months.

Above: several harvestman eggs and a young hatchling

When threatened, harvestmen often bob up and down erratically in an effort to confuse their attackers. They also have several other defense mechanisms, including pungent, foul-tasting secretions, the ability to "play dead," and autotomy, which is the ability to discard one or more of their own limbs in order to escape from predators.

Above: the photo at the top shows an unidentified harvestman from family Cosmetidae, while the photo on the bottom shows a species from genus Gnomulus

Harvestmen are completely harmless to humans. Their mouthparts are far too small to penetrate human skin, and contrary to popular belief, they do not have the "world's deadliest venom" -- in fact, they don't produce any venom at all.

Above: genus Obidosus

Sources & More Info:

BioOne: Fungus and Fruit Consumption by Harvestmen and Spiders: the Vegetarian Side of Two Predominantly Predaceous Arachnid Groups

Laboratory of Arthropod Behavior and Evolution: Harvestmen

Argo Biology: Citizen Science Reveals How Devoted Harvestman Dads Evolved Again and Again

NBC: Daddy Long-Legs Paternal Care Pays off in Longer Life, More Sex

PLOS One: Paternal Care Decreases Foraging Activity, but Does Not Impose Survival Costs to Caring Males in a Neotropical Arachnid

Gulo in Nature: Are Daddy Long-Legs Venemous?