11.02.2022

This is what a fertilized egg looks like shortly before hatching

Often we are asked how to tell if tarantula eggs are fertilized. In this post from Dec. 16, 2021 here on our Theraphosid Research Team Webpage, we had shown an unfertilized egg. As you can easily see, you can't see any development of body structures inside the egg. You can only see the yolk clods and perivitelline fluid. In comparison, Pic 1 shows a developed and fertilized egg shortly before the prelarva hatches. The segmented body of the spider is clearly visible. On the coxae of the dorsal palps (red arrows), the cuticle hooks or so-called "egg teeth" are conspicuous (Pic 2, green arrows), which tear the chorionic sheath when the embryo hatches. According to Foelix, "hatching enzymes" from the pedipalpal glands may also prepare this process. During the simultaneous first molting at hatching from the egg, these cuticle hooks disappear or are not newly formed, as can be seen in Pic 3.

Reference:

Foelix, R. (2010): Biology of spiders. Oxford University Press