Encore - Spider Webs in Dominican Amber
January 04, 2020
Today and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.
Photographer: Mila Zinkova
Summary Author: Mila Zinkova 
Shown above are microscopic images of twenty-million-year-old spider webs found in Dominican amber. The bubbles are glue droplets. Such droplets, usually found in the spider webs built by araneoid spiders, are used to capture prey. But, how could these glue droplets be preserved in amber if both resin and glue are fluids? According to Dr. Samuel Zschokke, the resin that covered these threads had a low viscosity; otherwise, the droplets would probably have been destroyed by the force of the resin flow.
Glue droplets in Dominican amber differ in size more than in other types of amber. The varying sizes can largely be explained by the availability of water, either due to the variable water content or to the variable water permeability of the resin. Because the glue droplets are highly hygroscopic, any water in close proximity to them will be absorbed, leading to their observed increase in size. Zschokke states that perhaps the reason why the size variability of the droplets in Dominican amber is higher than in other types is a result of the botanical origin of the resin: Whereas the older ambers stem from coniferous resin, the origin of Dominican amber is a deciduous tree.
The two photos are of the same piece of amber but taken from a different angle. The second image is a close-up of glue droplets showing what appears to be a trapped insect. This twenty-million-year-old insect is twice unhappy; first it was trapped in a glue droplet, and then in tree resin.
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