Arachnids: Reproduction & Adaptations

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

The world of arachnid reproduction is a world like no other. This lesson will delve into this bizarre and fascinating world, exploring examples and adaptations.

Arachnid Defined

Imagine a world where reproduction included ripping off limbs and cannibalism. Yeah, it doesn't sound particularly dreamy, does it? But these behaviors, along with a whole bunch of other weird stuff, is the making for a romantic evening if you are an arachnid. Before we delve into their sex lives, it's worth noting that an arachnid is a carnivorous (meat-eating) wingless animal in the Arachnid class. Arachnids include spiders, mites, scorpions, daddy long legs and ticks.

Arachnid Reproduction

Arachnid reproduction is quite varied, depending upon the species. For example, the blue-faced peacock spider gets jiggy, dancing about and sticking his legs in the air, all to impress the ladies. In a less romantic move, the female wolf spider will consume her mate after the deed is done. And the orb-web spider has a peculiar mating tactic. The male will cut his genitals off, leaving them stuffed inside the female so other males cannot mate with her.

Freaked out? Don't worry, it's not all weird. Let's explore the basics of arachnid mating. Since most arachnids live alone, finding a mate can prove challenging. In some species, females release pheromones, or chemicals that are used as a means of communication. In this case, the pheromones tell the males that an available female is in the region.

Once a male locates a female, he may have to fight off other males and then court her. As we mentioned with the blue-faced peacock spider, this might include a dance. Dancing is seen in scorpions as well, as they undergo a mating ritual known as promenade à deux, where the male grabs the female's pincers and leads her around. Daddy long legs also have a dance of sorts where the male grasps the female, and then the two shake legs, bite each other and occasionally rip off legs.

Sometimes the mating rituals result in the loss of legs in arachnids like the daddy long legs
daddy long legs

If a male wins the female over, the real action can begin. The reproductive organs for the male and the female are located in their back ends. In some species, the male will deposit a sperm packet (called a spermatophore) and then pick it up with his pedipalps, which are an additional appendage. Using his pedipalps, he will insert the sperm packet into the female's genital opening. Or sometimes, the female will insert the sperm packet herself.

pedipalps
pedipalps

The female may or may not use the sperm right away, with some species storing the sperm until she is ready to have her eggs fertilized.

Adaptations: Sexual selection

Now that you have the basics, let's check out adaptations arachnids have evolved in the bedroom. The focus here is sexual selection, which means one sex selects certain traits in the other sex and/or one sex competes with the same sex to get a mate.

You see this all of the time in the animal world. For example, in birds, a female peacock (called a peahen) will choose a male with the best tail. Or in the deer world, two male moose will use their antlers to fight and win over a female moose.

Arachnids do both of these things. In some species, the female will choose the best male or males will compete with one another. The evolutionary benefit here is, the male (or female) that is able to perform a fancy dance, or fight off a competitor, or show off flashy colors, is likely healthy with good genes. Therefore, the arachnid is finding the best mate with the best genetic material.

For example, the males of the red velvet mite will build a 'love garden' for the females. If the female approves of the garden, she will mate with him. The ability of the red velvet mite male to build a good love garden is related to his health (a weak red velvet male isn't apt to build a very impressive garden).

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