Why is my flat a woodlouse graveyard?

Pillbug, slater, parson’s pig, roly-poly or, apparently in Guildford and Guildford only, cheesy bobs. A woodlouse by any other name would apparently taste of “strong urine” — not that anyone’s recommending testing that one out. Whatever you call them, woodlice are probably the best-known terrestrial crustacean. There are currently 3637 species listed worldwide and we are lucky to have 35 species native to the British Isles.

The conundrum presented here is: the bottom few steps of my flight of stairs are regularly covered in dead woodlice. I never see a live one and they never seem to make it past about the fifth step, so what’s going wrong? They say to write what you know and at the moment I know sitting in my flat, so here we go.

Firstly, a bit more about the situation. The stairs start at ground level with a door which leads onto a concrete car park with a large ivy plant, several wheelie bins, and some broken drainpipes nearby (I’ll come back to why these are important later). The stairs consist of two flights and are carpeted, there is no central heating, and a small condensation issue. Whilst it looks like I’m just using this to vent about my flat, these are all relevant. I’d mention its excellent location, but I don’t know if woodlice need a fast train into London twice an hour.

DISCLAIMER: the author accepts that woodlice are not insects but found that changing the name of the blog to “Arthropods and that” would be an unnecessary faff.

Question 1: where do woodlice normally live?

Firstly, we need to understand the normal habitat of woodlice. There are hundreds of reports of different habitats in the UK alone, including beaches and cliffs, but the top three (in reverse order) are: garden, woodland, and grassland. Woodlouse diets typically consist of decomposing plant material, such as from urban plants and even food scraps. As their name suggests, woodlice can also digest cellulose from wood, but unlike termites, are not a serious risk to the integrity of wood in houses. It makes sense that parts of your house near a garden or cellar where there might be a lot of plant material would be the perfect starting point for woodlice.

Question 2: can woodlice climb?

We’ve established why woodlice are entering the home but how are they getting up the stairs if they normally tend towards the low spots? A 1990s article in New Scientist reported very similar observations to my flat, but in their case the woodlice were climbing up the corner between two walls and only getting so high before they died. Woodlice can climb on rough surfaces, which in their natural habitat would aid them climbing over organic material and up trees. I am blessed with carpeted stairs which would help them grip when climbing.

As the saying goes, however, what goes up must come down, and if they are able to climb up, why are they then getting stuck? I think there are likely two options: 1- most woodlice survive and climb down but I just don’t see them; 2- something is causing them to die at the peak of their climb. In the article I mentioned earlier, the author suggested that the humidity of an indoor room was killing the woodlice.

Question 3: do woodlice need as much water as lobsters to survive?

Woodlice, like many other invertebrates, need damp conditions. Woodlice normally absorb water from their food, which we do, through transpiration from moist air, as is common in other invertebrates, and through their anus, which we do not (no judgement if you do). When the humidity of the air around them is low, woodlice can lose large amounts of water through transpiration which, if they can’t find a new source of moisture, can be deadly. Possibly the further up the stairs towards warmth the woodlice are, the lower the relative humidity. If there is a steep gradient from the wet outside up the stairs, by the time the woodlice have climbed up a few stairs they are starting to dry out and with no further sources of water they desiccate fully.

Question 4: but why me?

If woodlice like dark and damp conditions so much, why do they keep coming into my home, which is surely warmer and drier than outside? Whilst that is probably true most of the time, it’s worth considering that climate constantly fluctuates. When I first moved into this flat in August it was warm and dry outside, so my dark and cool stairwell would have been deeply preferable. As I write this in January with the River Medway quietly flooding a few hundred meters away, there aren’t as many woodlice on the stairs. Possibly they’ve found somewhere safer for themselves. If so, I am glad of that.

Question 5: is there anything I can do to prevent this?

Woodlice aren’t a household pest, so any interest in keeping them out I have is purely based on preserving their life. I suppose I could leave small dishes of damp tissue paper out to allow them to rehydrate if humidity is the issue. I expect my front door functions like a lobster trap: woodlice are able to easily enter but not to leave. Try as I might, I can’t seem to get into the mind of a woodlouse to understand how they would come and go, so I think my only option might be to prevent them from climbing the stairs to their doom.