SPIDERS

There are a multitude of spiders in the Lobau that I haven’t even begun to investigate. Often the things you notice as you walk are the various webs, particularly on the open grassland areas where insect life is abundant, insects being a main source of food for spiders.

Some basic biology – short and simple!

Spiders, like insects, are invertebrates , that is they have no internal skeleton, instead an outside protective ‘shell’ (exoskeleton) of a substance called chitin. The body is typically segmented and divided, unlike insects, into 2 parts; the head and thorax form a single unit, the cephalo-thorax, with sensory organs (eyes, antennae), mouth parts, including fangs that produce venom and for injecting digestive juices into their prey in order to pre-digest them. It also bears 4 pairs of legs. The abdomen contains the reproductive and other vital organs and a spinneret at the tip. This extrudes silk used to spin webs for catching prey and to make nests or cases that protect the eggs during development.

Unlike insects, there are no extensor muscles in the limbs, which operate instead by hydraulic pressure. This is why the legs of a dead spider curl up.

As most spiders are predatory, the species has evolved a courtship procedure mainly functioning to identify the male and prevent the female from accidentally killing and eating her partner. It usually succeeds, though not always! Some spiders hypnotise the females, some are simply too small to be considered as worthwhile prey.

Fertilization is internal but indirect, the male ejaculates his sperm onto a specially prepared sperm-web, then picks it up with special appendages (pedipalps) and inserts it into the female’s genital opening. The eggs are laid in nests spun from silk and in some species the females protect the young and even share food. All the larval stages occur within the egg so the young spiderlings are exactly like the adults although sexually immature. As they grow they must shed their cuticle (hard outer ‘skin’) – a new cuticle then hardens on the soft and expanded form (moulting).