Winter walking with DEPL
Sunny days are coming back! With the rising of temperatures, arthropods reappear: bees start looting flowers again, butterflies start to fly again, and spiders weave new webs or wander in search of prey… But during winter, where have they all been? It is impossible to give a global answer to this question, as there is that great diversity within arthropods. Winter is a dark time for them: too low temperatures can kill them, food resources disappear… Decrease in daytime (photoperiod) and low temperatures will trigger behaviours that enable them to spend the winter safe. The problem with cold is that liquids can freeze, and when it’s the fluids that are inside your tissues or even inside your cells, the freezing can damage or even kill you. Thus arthropods want to avoid or control this phenomenon. Three major families of strategies emerge: avoiding ice formation into tissues, tolerating and controlling ice formation into tissues, or fleeing winter.
Let’s get interested in insects first. The first type of winter strategy consists to avoid fatal ice formation in the body. The insect will enter a kind of hibernation (term to be reserved for other animals), which will be called “winter diapause”. Insects in general are animals that experience metamorphoses, so they may undergo winter under different stage: eggs, larvae, pupa or adults (for holometabolous insects, i.e. full metamorphosis), eggs, larvae or adults (for heterometabolous insects, i.e. incomplete metamorphosis), eggs, juveniles or adults (for ametabolous insects, where the juvenile looks like the adult). First of all, the insect will look for a place where it will be able to partially isolate from the cold. For adults and larvae, this kind of place is legion. They can choose to hide in cracks, under the trees bark, underground, alone or in compact masses, in the ground litter… For motionless instars (pupae and eggs) it’s the same, adults will lay eggs in places that will protect them from the cold, while larvae will choose a comfortable place to transform into a pupa. Secondly, the insect metabolism will decline to a minimum level (what is called a diapause). Finally, the insect will produce special molecules to avoid ice formation in tissues; some of them will even producing polyol molecules such as glycerol, which is used especially in antifreeze fluids. The second type of strategy is to control how ice forms in tissues, to avoid damage. Generally, these insects will tolerate ice formation in extracellular spaces, but some of them can tolerate ice formation within their cells. Insects adopting this strategy will produce protein that serves as ice nucleus, i.e. around which liquids will be able to solidify. Sometimes it’s microorganisms that will play this role! However, just because they can tolerate a certain level of ice in their tissues, doesn’t mean they’ll survive a massive and rapid solidification of their liquids: this must be progressive and targeted. Finally, the last type of winter strategy is to flee winter by migrating to warmer areas, like do migratory birds. Relatively unused if we compare to the two others, this strategy is famous for being put in place by the American butterfly Monarch, Danaus plexippus.
For spiders, there are no metamorphoses; we have an “ametabolous” development. Just like insects, spiders fear too low temperatures and don’t seem to withstand ice formation in their tissues, also they will adopt the first strategy we saw for insects. They will go into winter diapause by hiding themselves from the cold; they can even lock themselves in thick silk lodges, allowing them to isolate themselves even more from the cold. They can also synthesize molecules to avoid freezing. Most spiders in France are annual, i.e. they only live about a year and adults die shortly after laying or after eggs hatching. Other spiders may have slightly longer life cycles (biennial, triennial) and others have much longer life cycles, as in mygalomorphs. Thus, most of our French spiders will diapause as juveniles, some others as adults, whereas spiders spending winter as eggs appear to be rarer. Some spiders, such as Philodromus, can hunt even in low temperatures or even with slightly negative temperatures as is the case for Anyphaena accentuata. Unlike manyinsects, spiders are more sensitive to temperature variations, and when mercury goes up a bit, they can come out of hiding, either to change their location or to try to hunt.
I’m not used to going out for pictures in winter: it’s cold, there’s almost nothing to photograph, and… it’s cold (yes I don’t like the cold)… So, the walking of the 11 January that I performed with the French naturalist association Des Espèces Parmi’Lyon was a great first for me (RIP to my fingers who passed away due to the cold ambient and the holding of the metal tube of my camera). With the small group of brave people who were with us, we lifted trees bark to discover the wildlife that had found refuge under it. And it paid off because not only did we find some interesting species, but I found two spider species that I had never met before!
One of the first animals we found was a pseudoscorpion; pseudoscorpions being an order within the Arachnida, just like spiders. They look like tiny scorpion without their tail. Some of them are frequently found under trees barks, and it’s difficult to go further than the order in the identification process.
Then we found some spiders. In a thick silk lodge as usual, a yellow Cheiracanthium sp. (Cheiracanthiidae) which was numbed by the cold. Under another tree bark piece, we found a new species for me, Porrhoclubiona leucapsis (Clubionidae) in a silk lodge, surrounded by a Corythucha ciliata (Tingidae) and two Arocatus roeselii (bugs belonging to the family Lygaeidae). Another Clubionidae was found: Clubiona cf. corticalis, the immature palpal bulbs meaning it’s a juvenile male, and we also found the second new species for me: Harpactea hombergi, a red Dysderidae with normal chelicerae and annelated legs!
We also found a beetle: Stenomax aeneus (Tenebrionidae)
To end, some pics of the walking:
Last update: April 5, 2021