Harvestmen

Typical Harvestman or Harvest Spider
Photo: J. Kalisch - UNL ©

Harvestmen, sometimes called harvest spiders, are often confused with the true spiders, but are easily distinguished from the latter by their globular body which has no obvious constriction or 'waist' between the front section (the cephalothorax or prosoma) and the hind section (the abdomen or opisthosoma). Also, unlike true spiders, the abdomen is clearly segmented and lacks spinnerets (silk-producing organs) at the tail-end. Harvestmen possess the usual arachnid appendages - chelicerae (jaws) and palps (leg-like sensory structures) at the front, and four pairs of walking legs articulated to the cephalothorax. Most species have very long legs, with the second pair always the longest. There are two simple eyes, often perched on a raised turret, near the middle of the cephalothorax.

The harvestmen most frequently seen are species of Opilio, Odiellus and Leiobunum that live in hedgerows, parks and gardens amongst rough vegetation or on tree trunks, walls and fences. All are moderately large, the body up to about 10 mm long, and more or less brownish in colour, sometimes with a darker saddle-shaped mark on the back (similar to the example shown opposite).

Most species are nocturnal, though often seen resting on walls and fences by day, with legs spread widely and almost invisible. They produce neither silk nor venom, and thus are quite harmless with no poisonous bite or sting. Apart from trusting to their dull colouring as camouflage, most of the familiar forms are quite active and largely rely on speed to escape danger, at the same time emitting an odorous and distasteful fluid from defence glands situated near the base of each front leg. Harvestmen feed on a wide range of living and dead animal matter, mainly comprised of small invertebrates (insect larvae, mites, young spiders, etc., or their dead remains), although they sometimes also attack juicy plant matter, primarily for its water content. More often they obtain water from dewdrops on vegetation. Most species have an annual life cycle, usually passing the winter as eggs and maturing in late summer - hence their common name.

More pictures of Harvestmen (and other arachnids) at the Department of Entomology, University of Nebraska-Lincoln (UNL).