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Arachnid

Arachnids are a group of invertebrates which are distinct from insects in that they have eight legs and lack antennae and wings. They also have two extra pairs of appendages, the chelicerae and the pedipalps, which have various uses, such as feeding, movement and defence. When we say ‘arachnid’ most people think of spiders but there are many other organisms which make up the arachnida class of animals, such as ticks, harvestmen and mites.

What do arachnids do in my garden?

Since most arachnids are carnivorous, their main use in the garden is to control insect populations. They maintain a balanced ecosystem in the garden by feeding on insects and other small organisms. There would certainly be a lot more pests flies buzzing around biting us and damaging crops if there were no spiders.

Many arachnids, in particular mites, can be pests themselves though. They make up the largest portion of arachnids and some species feed on plants, whereas many others are parasitic. Ticks are bloodsuckers which carry harmful diseases. They can cause problems for pet owners as dogs and cats often pick them up when running in long grass. On the whole though, arachnids should be encouraged into the garden as they make up an important part of any garden’s ecosystem.

Spider on web with eggsHow do arachnids catch their prey?

Arachnids have a variety of ways to catch their prey. Many spiders use webs made of strong and sticky silk which catch flying insects. The spiders avoid getting stuck themselves by making certain parts of their web non-sticky. They use the non-sticky parts to move around the web and debilitate any prey caught in its sticky embrace before it can escape.
Others, such as wolf spiders or jumping spiders, hunt their prey without the use of webs, preferring to lie in wait and ambush passing animals. The arachnid subdues its prey with its powerful front legs and a bite, which often injects venom. Once the prey is disabled, arachnids secrete digestive juices onto it, dissolving it into an easy-to-drink soup. They have a specialised muscular ‘pump’ behind the mouth opening which allows them to suck up their meal.
Other arachnids, such as scorpions, use a venomous stinger or strong crushing claws to disable their prey before eating it. Pseudoscorpions are much smaller than scorpions but nevertheless still catch mites and other tiny critters using their claws, some of which contain poison held in small glands.
Some spiders, such as Norfolk’s Fen Raft Spider, can skate on the surface of still waters. They hang on the water’s surface until they detect movement underneath from insects or even small fish. They dive down and grab the unsuspecting animal, making for a watery meal.

How do arachnids reproduce?

Most arachnids reproduce by transferring the sperm in a package called a spermatophore across to the female, often during a complex mating ritual. More often than not, the pedipalps are used in reproduction to transfer the sperm to the female. Most arachnids lay eggs but scorpions give birth to live young. Some scorpion species do produce eggs but these develop and hatch within their mother’s body and live young are born.

Arachnid Facts
  • Arachnids have been round for much longer than mammals and even reptiles, the earliest dating back more than four hundred million years!
  • Arachnids normally live on land but some species live underwater where they keep themselves alive by surrounding themselves in a large bubble of air
  • Many arachnids have a series of fine hairs covering their bodies, providing them with an enhanced sense of touch
  • Some young spiders travel good distances by producing silk until they are picked up by the breeze. You can see them on breezy days floating directionless through the air
  • Several cultures around the world consider arachnids to be a delicacy. For example, in some African countries, tarantulas are captured and roasted over an open fire for their nutritious flesh
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