Beneficials on farmland: identification and management guidelines (HGCA Summer 2008)

Spiders and harvestmen (Arachnids)

Arachnids are not insects; they have four pairs of legs, no wings and no antennae. They have only two body regions.

There are about 640 species of spiders in the UK. Spiders are carnivorous and are unique in having a spinner near the hind end of the abdomen which produces silk. Some spiders spin webs which are used as snares. Some lie in wait for their prey and others actively hunt.

Harvestmen are closely related to, and easily confused with, spiders. In harvestmen the two parts of the body are broadly joined, whereas in the spiders the body is clearly divided into two parts joined by a narrow stalk. Harvestmen have only two eyes whereas spiders have six to eight.

Spiders and harvestmen are very efficient pest predators. However, they are very sensitive to pyrethroids. Both can be important for bird diets.

Comb-footed spiders (Theridiidae)

  • Great variety of shapes and colours
  • Most have abdominal pattern
  • Legs have few spines
  • Uses individual sticky catching threads or criss-cross strands on bushes or trees to trap prey

Theridion mystaceum

Wolf spiders (Lycosidae)

  • Hunting spiders, mostly at ground level but occasionally on low vegetation
  • Mostly brownish, but attractively marked
  • Clothed in dense hairs
  • Good runners and can jump
  • Females conspicuous from May/June onwards with brown or greenish-blue egg sacs

Pardosa palustris

Orb web spinners (Tetragnathidae)

  • Spin orb webs
  • May also hunt
  • Elongated body with long legs

Tetragnatha extensa

Money spiders (Linyphiidae)

  • Largest European family
  • Small grey or black-bodied spiders
  • Hunting or web building
  • Drift through air on strands of silk
  • Consume aphid BYDV vectors on ground in autumn

Money spider (Erigone spp)
Webs of money spiders typically trap around 30% of aphids flying through the crop as well as wheat blossom midge adults and other small flying insects.

Crab spiders (Thomisidae)

  • Crab-like, with first two pairs of legs longer than rest
  • Can walk sideways as well as forwards and backwards
  • Most sit and wait for prey

Xysticus cristatus

Harvestmen (Opiliones)

  • 24 species in Great Britain
  • Oval body shape
  • Mostly nocturnal feeders
  • Actively hunt prey

Mitopus spp

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