Zoologist Jess French takes a look at some spiders, then accompanies a group of children to have a look for webs and eggs.
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Saturday, August 20, 2022
Wednesday, August 17, 2022
Eyes of the Spider
Spiders have primarily four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The principal pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However, in spiders these eyes are capable of forming images. The other pairs, called secondary eyes, are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the principal eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum, and wolf spiders can be spotted by torchlight reflected from the tapeta. On the other hand, the secondary eyes of jumping spiders have no tapeta.
Other differences between the principal and secondary eyes are that the latter have rhabdomeres that point away from incoming light, just like in vertebrates, while the arrangement is the opposite in the former. The principal eyes are also the only ones with eye muscles, allowing them to move the retina. Having no muscles, the secondary eyes are immobile.
The visual acuity of some jumping spiders exceeds by a factor of ten that of dragonflies, which have by far the best vision among insects. This acuity is achieved by a telephotographic series of lenses, a four-layer retina, and the ability to swivel the eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.
There are spiders with a reduced number of eyes, the most common having six eyes (example, Periegops suterii) with a pair of eyes absent on the anterior median line. Other species have four eyes and members of the Caponiidae family can have as few as two. Cave dwelling species have no eyes, or possess vestigial eyes incapable of sight.
Read more, here.
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Sunday, August 14, 2022
Spiders
Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every land habitat. As of August 2021, 50,266 spider species in 132 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
Anatomically, spiders (as with all arachnids) differ from other arthropods in that the usual body segments are fused into two tagmata, the cephalothorax or prosoma, and the opisthosoma, or abdomen, and joined by a small, cylindrical pedicel, however, as there is currently neither paleontological nor embryological evidence that spiders ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused cephalon (head) and the thorax. Similarly, arguments can be formed against use of the term abdomen, as the opisthosoma of all spiders contains a heart and respiratory organs, organs atypical of an abdomen.
Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.
Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-weaver spiders. Spider-like arachnids with silk-producing spigots appeared in the Devonian period about 386 million years ago, but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago, and are very similar to the most primitive surviving suborder, the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appeared in the Triassic period, before 200 million years ago.
Read more, here.
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Thursday, August 11, 2022
Learn Something About Silverfish!
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Monday, August 8, 2022
Reproduction and Life Cycle of Silverfish
Before silverfish reproduce, they carry out a ritual involving three phases, which may last over half an hour. In the first phase, the male and female stand face to face, their vibrating antennae touching, then repeatedly back off and return to this position. In the second phase, the male runs away and the female chases him. In the third phase, the male and female stand side by side and head to tail, with the male vibrating his tail against the female. Finally, the male lays a spermatophore, a sperm capsule covered in gossamer, which the female takes into her body via her ovipositor to fertilize her eggs. The female lays groups of fewer than 60 eggs at once, deposited in small crevices. The eggs are oval-shaped, whitish, about 0.8 mm (0.031 in) long, and take between two weeks and two months to hatch. A silverfish usually lays fewer than 100 eggs in her lifetime.
When the nymphs hatch, they are whitish in colour, and look like smaller adults. As they moult, young silverfish develop a greyish appearance and a metallic shine, eventually becoming adults after three months to three years. They may go through 17 to 66 moults in their lifetimes, sometimes 30 in a single year—many more than most insects. Silverfish are among the few types of insect that continue to moult after reaching adulthood.
Read more, here.
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Friday, August 5, 2022
Silver Fish
Read more, here.
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Tuesday, August 2, 2022
Why Cockroaches Are So Hard To Kill
Cockroaches are one of the most widespread and resilient creatures on this planet. They are practically everywhere around us, hiding in the walls, sewers, and perhaps your cupboard. They are also one of the most hated creatures by humans. If you are like most people, you will become determined to kill all of the roaches when you see them in your house. Despite such hatred towards them, how do cockroaches manage to thrive all around the globe?
Science Insider tells you all you need to know about science: space, medicine, biotech, physiology, and more.
Jeff Verges/Owner/Operator
742 Santa Anita Court
Eugene, OR 97401
541-688-0580 Eugene
503-371-8373 Salem
Subscribe to:
Posts (Atom)