- Location
- Lincolnshire
Slimer data collection
- Thread starter Trotter
- Start date
Good find! Thank you for sharing, it will be interesting to see how many other Sleuths find slugs under their trap rocks.
- Location
- Kent
Ah, I've been finding worms under the stones!
- Location
- Kent
Having applied more slug pellets than I have for many years I am now catching lots of tiny slugs as opposed to larger ones, so I guess the eggs have still been hatching - what timescales does a slug life cycle operate over?
This is a great question - I wonder if @Repwal would know the answer?
As you will no doubt have realized already nothing is straightforward with slug biology, so the answer is that it depends on environmental conditions, time of year and a variety of other factors!
In general, however, slugs such as the grey field slug (thought to be the main but not the only arable pest species) can breed all year round so your thought that eggs are currently still hatching is almost certainly correct. There are two overlapping generations usually with peaks of egg laying in March-April and September-November. When the eggs mature they turn white and can take from 2 weeks to a month to hatch, depending on the environmental conditions and the time of year at which they are laid. It can take 5 months to hatch if eggs are laid in late winter. Eggs laid in late autumn can overwinter, and may not hatch until the following spring (but they can hatch earlier, again if environmental conditions favour them.
In case it is of any interest, the following gives a little more detail regarding the life cycle:
The grey field slug (GFS – one of the slug species in the photograph posted last Friday by “Terther”,) has two main peaks of reproductive activity, one in spring and one in autumn, however, it is an opportunistic species which reproduces whenever favourable mild, wet conditions occur, resulting in overlapping generations/life stages throughout the year. In contrast, some other species such as Arion spp. (roundback slugs – the other slug in the photograph by Terther) have an annual life cycle with a single peak of reproductive activity occurring in late spring to early summer. The annual pattern of GFS with two reproductive peaks, coupled with their response to environmental cues such as temperature and moisture, enables populations to increase rapidly when environmental conditions are favourable, a response that is critical in disturbed environments such as arable fields. Although slug eggs are widely known to be susceptible to desiccation, there is evidence that GFS can mitigate for this by adjusting the number of eggs laid depending on the environmental temperature and moisture conditions maximising population increases when conditions are optimum. Whilst eggs are susceptible to desiccation, the juveniles have the lowest rates of overwintering survival; eggs which fail to hatch by the end of the autumn may remain dormant until the following spring. Most slug species have three post-hatching life stages; infantile/neonates (rapid growth), juvenile (medium growth) and adult (minimal growth) although GFS only have two post-hatching life stages, namely the juvenile and adult stages. Slugs are hermaphrodites. During the juvenile stage GFS are typically males, with older adults taking the female role. In the absence of juveniles, adult slugs can also take the male role to prevent a reduction in reproduction and so population size. The faster growth rate during the juvenile stage of GFS reduces the time that young slugs are at risk due to extreme environmental conditions or predation.
In general, however, slugs such as the grey field slug (thought to be the main but not the only arable pest species) can breed all year round so your thought that eggs are currently still hatching is almost certainly correct. There are two overlapping generations usually with peaks of egg laying in March-April and September-November. When the eggs mature they turn white and can take from 2 weeks to a month to hatch, depending on the environmental conditions and the time of year at which they are laid. It can take 5 months to hatch if eggs are laid in late winter. Eggs laid in late autumn can overwinter, and may not hatch until the following spring (but they can hatch earlier, again if environmental conditions favour them.
In case it is of any interest, the following gives a little more detail regarding the life cycle:
The grey field slug (GFS – one of the slug species in the photograph posted last Friday by “Terther”,) has two main peaks of reproductive activity, one in spring and one in autumn, however, it is an opportunistic species which reproduces whenever favourable mild, wet conditions occur, resulting in overlapping generations/life stages throughout the year. In contrast, some other species such as Arion spp. (roundback slugs – the other slug in the photograph by Terther) have an annual life cycle with a single peak of reproductive activity occurring in late spring to early summer. The annual pattern of GFS with two reproductive peaks, coupled with their response to environmental cues such as temperature and moisture, enables populations to increase rapidly when environmental conditions are favourable, a response that is critical in disturbed environments such as arable fields. Although slug eggs are widely known to be susceptible to desiccation, there is evidence that GFS can mitigate for this by adjusting the number of eggs laid depending on the environmental temperature and moisture conditions maximising population increases when conditions are optimum. Whilst eggs are susceptible to desiccation, the juveniles have the lowest rates of overwintering survival; eggs which fail to hatch by the end of the autumn may remain dormant until the following spring. Most slug species have three post-hatching life stages; infantile/neonates (rapid growth), juvenile (medium growth) and adult (minimal growth) although GFS only have two post-hatching life stages, namely the juvenile and adult stages. Slugs are hermaphrodites. During the juvenile stage GFS are typically males, with older adults taking the female role. In the absence of juveniles, adult slugs can also take the male role to prevent a reduction in reproduction and so population size. The faster growth rate during the juvenile stage of GFS reduces the time that young slugs are at risk due to extreme environmental conditions or predation.
This is an interesting observation and one that we have only found occasionally in earlier experimental work. It would be interesting to know if this is a regular occurrence or alternatively whether it was noticed after periods of heavy rain/very wet field conditions. I ask because although slugs are known to favour damp conditions, if the soil becomes waterlogged then they are repelled to avoid increased mortality rates in the population. I wonder (and it is pure speculation so don't quote me) whether the slugs are being arrested by the refuges on top of the trap as they help them avoid the worst effects of high water content in soils. Could you (or anybody else) comment on soil conditions at the time you noticed this please?
Should we be counting the slugs found under stones on the trap?
- Location
- Lincolnshire
I'd say some areas of the field were wetter than others but I can't say i'd noticed a correlation between this and where the slugs were hiding under the stones. The field in general has been wet but by no means at field capacity. Perhaps there were more during the second count I did but I wouldn't be able to prove this. I did notice a difference between type of stone used to weigh the traps down and slug numbers. Flinty or angular stones certainly harbored more slugs than round or darker stones. I did decide to count the slugs underneath the stones as I felt they were within the area being assessed - technically the surface area was increased by doing this but felt it a more accurate count than not including them since they were within the data collection zone. Perhaps something to think about for future trial set up / data collection protocol? J
Interesting to read all of the above. Just thought it would be worth adding my observation about the weight of the 'weighing' stone. Where large bits of concrete or anything really heavy has been used it has almost sealed the trap in the moist soil and little to no slugs are ever there. Where I have heavier stones I try to balance them on one edge to at least allow part of the trap to not be under such pressure... obviously you go back in a week and it hasn't worked. To add to Trotters point above; maybe uniform weights for the future.