Ice Age Ponds are important wildlife havens, due to their ephemeral nature and ancient existence. I am sure by now, if you have read our previous blogs, you have a good appreciation for these fascinating habitats (and if not, then check our other blogs out!) and what great places they are for protected species such as the popular Great Crested Newt, but have you heard about how they may play a role in the recovery of the extremely rare Medicinal Leech (Hirudo medicinalis)?

Medicinal Leeches, the UKs largest (and most colourful) leech was once found across the country. They have a rich history linked with British medicine, and were commonly used as medicinal cures during the medieval times. Even today leeches play an important role in medicine and are still used to increase blood circulation in some countries.

The medicinal leech is the only UK leech that can feed on human blood, and will feed on a range of species, most commonly frogs (both adult and tadpoles) but will also prey on cattle and deer. Unlike other leeches found in Britain. they are the only species capable of drawing mammalian blood and they have three jaws containing 100 teeth, growing up to 20 cm long!

However, like many of our country’s species, the numbers of medicinal leeches have plummeted, and they are now on the brink of extinction in the UK. Having once been found in abundance at hundreds of sites, there are now only three populations remaining. Causes of their decline was initiated by the medical trade, when millions of wild leeches were exported. In recent years, land use change, wetland drainage and loss of grazing have contributed to their rapid declines.

This unique species has become so rare that they are a global conservation priority, and are listed under a number of international legislations including Appendix II of the Conservation on International Trade in Endanger Species (CITES), IUCN Red List and Appendix III of the Bern Conservation.

In order to help preserve and protect this species, it is vital we have a clear understanding of where populations are, and if any historic populations could persist undetected. This is where the Ice Age Project Team come in!

One of our sites, located on a National Nature Reserve, has historically had medicinal leeches, however they haven’t been recorded for many years. In partnership with the Fresh Water Habitats Trust, our team and volunteers set out to perform a leech-specific survey to try and find out if these primitive creatures still lurked in the depths of this pond.

A leech specific survey – what does that entail? Let me enlighten you.

In order to attract a leech, you need to act like a tasty meal, and the best way to do this is to pretend to be a cow! In pairs, we surveyed 12 sites around the pond. One person from the pair would wade into the pond and splash a pond net around, imitating a drinking cow, for ten minutes. After this you stand and watch the water, scooping out any leeches you see swimming towards you.

Sadly, we did not find any medicinal leeches, although we did have a few duck leeches! We are still hopeful, as there are many factors which meant the leeches may not have wanted to come out and play that day. Leeches will only react to potential prey if they are hungry. As there had been cattle in the pond in the last few weeks, it is possible all the leeches were too full to investigate. Leeches are also more active in warmer water, and on the day of the survey the water was a bit on the cooler side (despite being mid-August!).

The team hopes to conduct an eDNA survey on the pond, which could pick up any medicinal leech DNA in the water, so we haven’t given up on our quest for the missing leech yet!

Thank you to all the volunteers who attended, and to the Fresh Water Habitat Trust for the online training you provided.