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Croaking Science – a ‘new’ species of leech predating amphibians

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Written by Andrew Smart, Head of Science & Research

Lawson, B. et al , 2024. Predation of anurans in southern England by Batracobdella algira, a leech previously unknown in the UK. Herpetological Journal. 34 221-227

Leeches are often identified as potential predators of the various life stages of amphibians and in the case of frogs and toads, four native species of leech have been identified as feeding on blood and one leech, Haempois sanguisuga, (the horse leech) are know to be predatory on froglets and toadlets.

Reports of leech infestation on a common toad in 2020 led the authors of this recently published paper to explore the occurrence of leech predation on anurans more widely.  A call for Citizen Scientists to report sightings led to 41 new records between 2020 and 2023.  The authors undertook a detailed review of the species involved, either through morphological or genetic identification, and found that in 2 of the 9 cases identified, the species was Placobdella costata, while in the remaining 7 of the 9 records where leeches were identified to species, the species was Batracobdella algira, a species previously unrecorded in the UK.

Dorsal and ventral view of Placobdella costata

The genotype of the animals collected corresponds with that of individuals from Tunisia and, along with a localised distribution in the south and south west, this suggests the possibility that it is a non-native invasive species. The authors suggest that possible routes of ‘invasion’ include release through animal or plant trade or natural long distance dispersal by birds.

Two other publications from 2016[1] and 2018[2] highlight the link between this leech species and cave salamanders in Sardinia, which suggest that the leech could parasitise newt species. The leech has been recorded on painted frog (Discoglossus pictus) and marsh frog ( Pelopphylax ridibundus) [3] in Morocco and has also be found to parasitize Bufo spiniosus in Tunisia[4] and Algeria[5], a possible pre-adaptation for parasitism of Bufo bufo in the UK.

There is no evidence of the leech being a problem for amphibians within its natural range but it will certainly be worth toad patrols and amphibian surveyors looking out for any new records of leech predation this coming breeding season and notifying the Garden Wildlife Health Project at ZSL of any new records.

References

Click to read more...

[1] Manenti, R., Lunghi, E., Canedoli, C., Bonaccorsi, M. and Ficetola, G., 2016. Parasitism of the leech, Batracobdella algira (Moquin-Tandon, 1846), on Sardinian cave salamanders (genus Hydromantes)(Caudata: plethodontidae). Herpetozoa, 29(1-2), pp.27-35.

[2] Lunghi, E., Ficetola, G.F., Mulargia, M., Cogoni, R., Veith, M., Corti, C. and Manenti, R., 2018. Batracobdella leeches, environmental features and Hydromantes salamanders. International Journal for Parasitology: Parasites and Wildlife, 7(1), pp.48-53.

[3] Mabrouki, Y., Ahmed, R.B., Taybi, A.F. and Rueda, J., 2019. An annotated checklist of the leech (Annelida: Hirudinida) species of the Moulouya River basin, Morocco, with several new distribution records and a historical overview. African Zoology, 54(4), pp.199-214.

[4] Hassine, J.B. and Escoriza, D.., 2014. Bufo spinosus in Tunisia: new data on occurrence, parasitism and tadpole morphology. Herpetol. Bull, 127, p.22.

[5] Merabet, K.. and Karar, M., 2021. First cases of predation of Bufo spinosus by two leech species in Algeria. The Herpetological Bulletin, 156(156), pp.38-39.

The midwife toad

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Written by Emma Byrne, Transforming Lives Trainee. 

What is a midwife toad and how did it get its name?!

Midwife toads are native to Western Europe and arrived in Britain at the end of the nineteenth century.  They are small and plump, about 5 cm (about half the length of the long edge of a credit card), with warty, mostly dull grey, but occasionally green or brown skin. The females sometimes have red spots on their flanks. They’re similar in appearance to common toads, except their snout is more pointed and the pupil of the eye has a vertical slit as opposed to the common toad’s horizontal split.

Midwife toads are nocturnal and have a very distinct call which sounds like a high-pitched beeping noise. This noise is very different from the croaking sounds produced by our native frogs and toads, and is exceptionally loud for a small toad, making it easy to track them down in the darkness.

So why the name midwife toad? This name stems from the toad’s breeding habits. The female expels a strand of eggs, which the male fertilizes externally. He then wraps them around his legs and carries the string of fertilised eggs on his back to protect them from predators in the water, hence the name “midwife”. The male will carry the eggs until they are ready to hatch, at which point they are deposited in shallow water.

So where can you find these delightful little toads? Midwife toads can be found throughout several different habitats from arable land, forests and wetlands. In the UK, they are mainly restricted to urban areas close to their initial release sites with populations across England and Wales including Bedfordshire, Yorkshire, Worksop and South Devon. That said, possible sightings have been made in other areas of the country, so ensure to listen out for that electronic beeping sound…there could be a midwife toad closer than you think!

To find out more about this species click here. 

Remember to record your sightings of native and non-native amphibians and reptiles on our free Dragon Finder app.

Reference: Stidston, R. (2012) Midwife toadlet. Available at: https://www.uksafari.com/midwifetoads.htm

Natterjack Toads (Epidalea calamita)

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Written by Eve Goddard, Transforming Lives Trainee. 

Natterjack toads are the lesser known of the two native UK toad species.

Smaller than the common toad, natterjacks are up to 7cm in length and have shorter legs, which they use to run in short bursts. Unlike the common toad’s bronze iris, natterjacks’ are bright green. Their most distinguishing feature is the yellowy stripe which runs down the centre of their back.

Their common name is said to come from their distinguished rasping call which can be heard up to two km away. Males take advantage of this in spring, the louder their call, the more chance they have of attracting females.

You can hear their call by clicking this link (© Slitere National Park)

 

Habitats

Natterjacks live in saltmarsh, heathland and coastal areas. They use warm freshwater ponds for breeding. One example being ponds that form in sand dunes. Their spawn is laid in singular rows, unlike the common toad’s double rows. In preferable conditions their spawn can mature very quickly – in as little as six weeks, which creates an evolutionary advantage for avoiding  predators, and leaving a pond that may be both porous due the sandy substrate and/or seasonal.

For hibernation in the winter, their shorter strong limbs come into play. They dig burrows in sand or light sandy soils. Natterjacks will also use the same technique in the summer to protect themselves from particularly hot weather.

 

 

Conservation

As one of the UK’s rarest amphibians, natterjack toads are a protected species by law, it is an offence to kill, injure, capture or disturb them; damage or destroy their habitat; or possess them or sell or trade them in any way. This also applies to larval stages and eggs.

Although their populations are few and far between, owing largely to habitat loss, there are some simple steps we can all take to protecting their habitats. When visiting saltmarsh, heathland or coastal areas taking litter home with you, keeping to designated footpaths, and keeping dogs on leads and out of ponds all helps.

Remember, if you spot a natterjack toad or any of our reptiles or amphibians – the Dragonfinder App will allow you record your findings and help us in our conservation efforts.

Preparing for Spring

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Written by Ellia Cobb, Transforming Lives Trainee. 

It’s almost springtime again! Reptiles and amphibians will be getting ready to come out of their brumation and begin their breeding season, so what can you do to help them? If you have a wildlife pond at home it is important to finish up any pond maintenance you might want to do before the weather starts to warm up. Disturbing breeding and egg-laying amphibians can be very harmful, so ensuring good pond maintenance is essential.

Preparing your wildlife pond for spring is a simple task as they don’t require much work. Cutting back reed and grass from the pond if it is too overgrown to allow more sunlight in can hugely benefit the pond, but remember to leave enough for the breeding amphibians! Another thing you can do is remove leaf litter and sediment build up from the pond to prevent a decrease in the water quality, but this should be done before spring. Anything that is removed should be left by the pond for a few days just in case any wildlife remains inside of it, this gives them time to make their way back to the water (please see our Just Add Water guide for further tips). 

Newts need vegetation to lay their eggs and toads and frogs need a safe place to lay their spawn away from predators.

The changing weather can be quite confusing for amphibians so it isn’t uncommon for them to start breeding earlier than expected, so don’t be alarmed if you spot any spawn or eggs quite early on. You do not need to move or disturb them. Newts need vegetation to lay their eggs and toads and frogs need a safe place to lay their spawn away from predators, so providing native pond plants and safe places for them to hide before spring starts is the best idea.

As for reptiles bramble, compost heaps, log piles, gorse and wooded areas are all places they may choose to breed in. This means that any garden maintenance shouldn’t be done during this time to prevent disturbance and endangerment.

You can find further information on how to make your gardens more wildlife friendly in our Idea Zone. 

 

Disease in Amphibians

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Written by Ellia Cobb, Transforming Lives Trainee

Disease is a huge issue for our amphibian population, Ranavirus and Chytridiomycosis being two of the main diseases that threaten our native species. It is thought that these diseases were introduced by non-native species being released into the wild. One third of all amphibians are at risk of extinction with heavy declines across the globe.

A frog with ranavirus (c) Dee Wilkinson

Ranavirus is somewhat new to the UK and is mainly found in common frogs, some of the symptoms are skin ulcers which are commonly seen on the skin around the legs and pelvic area. The frogs infected will also suffer from internal bleeding which you may only be able to identify from redness around the mouth and cloaca. Frogs may also show signs of lethargy, but they won’t always show obvious symptoms of this virus. Ranavirus is only active during warmer temperatures, but can be devastating to pond populations around summer time, it is fatal and can affect the entire pond population.

Chytrid infection has been responsible for mass mortalities within the UK’s amphibian population and in some cases, it has caused extinctions. Most native natterjack toad populations have tested positive for the infection, but seem to be unaffected. That however, doesn’t stop them from spreading it to other amphibian populations. Evidence suggests that chytrid causes death by preventing sufficient uptake of salts through the skin. Amphibians need these salts for their circulation and without this, their hearts cease to function. Symptoms of this include ulcers, reddening, shedding and unusual behaviours.

There are steps everyone can take to prevent the spread of amphibian disease:

  1. Do not transfer animals or plants from one pond to another. 
  2. Do not purchase wild-caught spawn, tadpoles or adult amphibians online. Not only is this against the law, but you do not know the origin of the animals. 
  3. Do not release pet/exotic amphibians into the wild. It is against the law and can cause severe damage to not only the released amphibian, but the local population too. 
  4. If you suspect disease in an amphibian, report it to Garden Wildlife Health

Amphibians In Urban Environments

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Written by Kaitlin Oliver, Transforming Lives Trainee

Amphibians in urban environments face a range of challenges due to the altered habitat, pollution and human activities associated with urbanization.

Urban development often involves the destruction of natural habitats which lead to the loss of breeding and feeding grounds for amphibians. Additionally, any remaining natural areas can become fragmented with lakes and woodlands being closed off by housing, making it difficult for amphibians to move between suitable habitats. This can lead to isolated populations and reduced genetic diversity, causing inbreeding.

Amphibians heavily rely on aquatic environments for breeding and larval development. Urban environments can expose amphibians to various forms of pollution, including chemical pollutants from runoff, air pollution and noise pollution. Amphibians have permeable skin that makes them sensitive to pollutants, leading to developmental deformities, immune system suppression and reduced reproductive success. Urban areas often have altered water bodies like unhealthy ponds, ditches and drainage systems that may be contaminated with pollutants, have fluctuating water levels, or lack suitable vegetation. These conditions can negatively impact amphibian survival rate and their larval survival.

Amphibians such as frogs and toads rely on using water sources such as lakes, rivers, forest ponds and garden ponds. Newts especially rely on healthy ponds to breed in. If you have space, adding a pond to your garden will not only help amphibians, but will also massively improve the lives of a variety of wildlife. Froglife has a booklet that you can download called ‘Just add water’ on our website if you are interested in building a pond suitable for amphibians.

Designing urban infrastructure with consideration for amphibians can make a significant difference. For example, creating artificial wetlands, amphibian-friendly green roofs, creating wildlife corridors, maintaining natural water bodies, implementing wildlife-friendly landscaping practices and constructing road barriers or tunnels to reduce road mortality can all provide fantastic habitats and mitigate the impacts of urbanization.

Citizen science is very important as it can help monitor the health and distribution of amphibians. If you have a pond that amphibians breed in or visit, please use our free Dragon Finder App to report your sightings. Roads and vehicles pose a significant threat to amphibians in urban areas, so another way you can help amphibians is through the Toads on Roads project, where you assist toads in your area with their spring migration journey crossing roads.

Urbanization poses numerous challenges for our declining populations of amphibians, however, there are opportunities for conservation and education. By implementing thoughtful planning, mitigation measures, and public engagement, it’s possible to create more amphibian-friendly urban landscapes and help protect these vital components of biodiversity.

 

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