Category Archives: Arthropods

Orb-weaving Spiders Eat Plant Pollen (And Their Own Webs)

We all know spiders as crafty predators, building sticky webs to snare unsuspecting insects as well as the occasional frog, mouse, lizard, or bird.  Then, as I learned it, they’ll wrap up their captured prey, inject it with digestive enzymes, and slurp up the resulting product.

Just look at this spider: creepy, and definitely bloodthirsty, right?

Araneus diadematus, courtesy of Frode Inge Helland via wikimedia commons.

Well, that’s what I always thought, anyway.  It turns out, though, that some spiders (like the orb-weaver A. diadematus pictured above, for one) eat more than just other animals.

Herbivory in Spiders: The Importance of Pollen for Orb-Weavers,” an evocatively named article recently published in PLOS ONE, explains that some spiders capture pollen in their webs, digest it externally, and slurp it up to the tune of 25% of their diets.  A side salad with every slab of steak, so to speak.  How genteel.  Anyway, the article shows convincingly that spiders’ pollen consumption is not just a fluke — through an array of experiments, its authors provide “direct proof that orb-weaving spiders (Araneidae) indeed feed on pollen captured in the sticky spirals of their webs and incorporate this into their body tissue, even when prey is available.”

The article is good reading.  In fact, I can’t resist sharing another fascinating detail of spider diets: “Orb-weaving spiders (Araneidae) take down and eat their webs at regular intervals, which enables them to recycle the silk proteins efficiently.”  I am happy I now know this, and I hope you are too.

I’ll close with the article’s abstract and leave it to you to click through and read for yourself if you like:

Orb-weaving spiders (Araneidae) are commonly regarded as generalist insect predators but resources provided by plants such as pollen may be an important dietary supplementation. Their webs snare insect prey, but can also trap aerial plankton like pollen and fungal spores. When recycling their orb webs, the spiders may therefore also feed on adhering pollen grains or fungal spores via extraoral digestion. In this study we measured stable isotope ratios in the bodies of two araneid species (Aculepeira ceropegia and Araneus diadematus), their potential prey and pollen to determine the relative contribution of pollen to their diet. We found that about 25% of juvenile orb-weaving spiders’ diet consisted of pollen, the other 75% of flying insects, mainly small dipterans and hymenopterans. The pollen grains in our study were too large to be taken up accidentally by the spiders and had first to be digested extraorally by enzymes in an active act of consumption. Therefore, pollen can be seen as a substantial component of the spiders’ diet. This finding suggests that these spiders need to be classified as omnivores rather than pure carnivores.

Reference:

Eggs B, Sanders D (2013) Herbivory in Spiders: The Importance of Pollen for Orb-Weavers. PLoS ONE 8(11): e82637. doi:10.1371/journal.pone.0082637

Glowing scorpions

Speaking of blue bioluminescence, did you know that scorpions and some other arthropods glow blue under ultraviolet light?  A fascinating post from Wired explains the mechanism and some reasons scientists have hypothesized for why these creatures glow as they do.  Below is an interesting excerpt from the post, but you’ll really want to click through to read the read the rest — and see the pictures.

For scorpions, the mechanism of the glow has been studied in more detail. Scorpions have “cuticular fluorescence.” Basically, compounds in their exoskeleton absorb and re-emit ultraviolet light as visible light (light humans can see). The exoskeleton of an arthropod is made from composite materials that are both strong and flexible. It’s the outermost layer, epicuticle, that produces the glow, and it seems to be something that changes chemically as the animals grow.

Two compounds are involved in scorpion UV fluorescence: beta-carboline and 4-methyl, 7-hydroxycoumarin. You might recognize coumarin as a common plant compound, and it’s often used as a perfume or in cinnamon flavors.