Underground life of Boettgerilla pallens


Boettgerilla pallens in the terrarium

Sometime in August 2011 – I have added soil from the garden into the terrarium. It is the plastic transparent box, vertically placed it has inner dimesions like this: 17 cm high, 8.3 cm length. The inner dimension (the width) is 28 mm. The box have the same dimensions as a box that you have allready seen in my previous post. I have placed one earthworm to the terrarium.

The same box but larger could be useful to watching earthwors. A Czech book for teenargers recommends box for earthworms like this: 30×30×2.5 cm. So my terrarium for slugs is probably too thick to easy wath the undergound life.


It was placed in absolute dark in cupboard those times without slug. The earthworm has been making earthworm burrows and it has been producing earthwom faeces.


16th September 2011 – I have collected one adult Boettgerilla pallens in the garden.

17th September 2011 – I have placed the slug into the prepared terrarium. I have added the second earthworm into the terrarium, because I have thought, that the one have not survived.


It is thought, that Boettgerilla pallens is afraid of direct light, so the three sides of the terrarium are placed in the mild shadow all the time. Maybe I should keep it in more darker place.


The slug has immeditelly moved into the center of the terrarium. It has been moving inside the soil at the same speed as it is moving over the surface of the soil.


I think, that it is resting in the upper part of small “caves”, when there are small caves available. At least I have seen resting my slug in such place few times.


Sometime I have found out, that there are in fact two earthworms in the terrarium. There are also two about 6 mm long millipedes (Diplopoda).


I have been adding food sources to the terrarium very rarely (about four times for the last 2.5 months). Food sources were fresh or rotting leaves of probably Common Dandelion Taraxacum officinale (rotting leaves were from other of my terraria inhabited with other gastropod species). When I have been adding food, I have been also adding some water. The terrarium is not water-resistant and when there is too much water, it will appear under the terrarium.


AnimalBase is claiming that the slug is feeding also on aerthworm faeces. If so, then Boettgerilla had always enough food.


I usually see no slug even if I will carefully check all transparent sides.


25th October 2011 – I have found out that there are at least two juvenile Boettgerilla pallens. The juvelines are white, while adults are grey.


Gunn (1992) studied the life cycle of this species. He have described eggs as transparent when laid and later white. There was not mentioned the size of eggs. Unfortunatelly I have seen no eggs. Juveniles hatch after 20-22 days at 17 °C. The temperature conditions in my room is 21 °C, because I live there. Adults survive egg-laying and die shortly after, but the can survive “for over a month”. I think, that my slug have laid the eggs. It is possible, that eggs or even such small juveniles were in the soil since August. Egg laying was recorded since August to October in Wales.


27th October 2011 – The adult Boettgerilla pallens is still alive.


2 November 2011 – I have taken photos of one juvenile. It was about 4 mm long.

The foot of juvenile slug:


3rd November 2011 – The adult Boettgerilla pallens is still alive.



(in Czech) Dobroruková J. & Dobroruka L. J. (1989). Malá tajemství přírody. Albatros, 177 pp., page 82.


Gunn A. (1992). “The ecology of the introduced slug Boettgerilla pallens (Simroth) in North Wales”. Journal of Molluscan Studies 58(4): 449-453. doi:10.1093/mollus/58.4.449 (the first page extract)


“Species summary for Boettgerilla pallens. AnimalBase, last modified 28 December 2008, accessed 8 September 2010.

How slugs fight against dehydration

I have put nine Tandonia budapestensis into fully transparent plastic terrarium with internal dimensions: 17 cm long, 8.3 cm width and 2.8 cm high. This transparent box (or any other transparent terrarium) seems to be useful for watching the behaviour of gastropods. They received a piece of skin of watermelon as a food source. They also received some water from water sprayer, but not too much because I was afraid of drowning of slugs. Approximately only centre of the box was sprayed once. There was nothing else in this terrarium. No substrate except of some small pieces of soil that were stinged to slug’s bodies during transport. No ventilation, but probably no loss of water in this closed artificial environment.

About one day later they were “sleeping” and they were clustered like this:


Two of them are not on the photo, because they were on the cover. Those two were also next to each other.


Similar photo of aggregation of slugs (of Limacus flavus) is on the page 470 in the 2001 book The biology of terrestrial molluscs.


This aggregation of slugs is explained as behaviour against loosing of water in drier environment. They are tightly packed to each other and they reduce the area of evaporation. (Snails do not do that, because they can retract to shells.)


I have taken the first photo at 18:57:33 very soon after the removing the cover of the terrarium. All slugs were sleeping and one was eating. Slugs have swiftly found out, that something has changed. After 1 minute 22 seconds (at time 18:58:55) they started to extend their tentacles and started to move.


Next days they did not make similar aggregation. It seems, that instead of that, they “discovered”, that they can be sitting on the watermelon and receive water through the body wall.


You can not see such behaviour if you will keep one, or two slugs in the terrarium.

When I have started to doubt that they will agrregate again and six days later after taking the first photo, I have taken these photos: