Holly Steel

The skin of adult crested newts is granular in appearance with a black or dark brown background colour with darker spots which in males extends onto the crest. It has very fine white spots on the lower flanks. As so often in nature it is the male great crested newt that is the colourful breed, doing its best to entice the female into courtship. Males have a very impressive jagged crest along their back that dips at the rear of the abdomen, and a smoother edged crest above and below the tail. Their crest decreases in size as the breeding season comes to an end. Males also have a white, silver or grey stripe running from the tail tip along the central, fleshy section of the tail that fades as it approaches the abdomen.

On land, the great crested newt appears virtually black, and in males the crest shrinks back against the body. The female lacks a crest and white tail stripe, but has a token yellow-orange stripe running along the bottom edge of the tail. Both sexes have a vivid orange or yellow belly with an irregular pattern of dark black spots or blotches.

The larvae of great crested newts can be distinguished from the other species by the presence of a filament at the tailtip and black blotches over the body, tail and crest. They can be very hard to tell apart when they are under 20mm in length. Great crested newt larvae are considerably larger, reaching a length of 50 – 90mm before metamorphosis (compared to 30 – 40mm for the smaller species).

Continental forms of crested newts are very difficult to tell apart from native British great crested newt without expert help and analysis. The release of exotic newts in the wild is unlawful and undesirable as they can have a negative effect on native species. After around 16 weeks, metamorphosis is completed when the gills and tail fins are totally resorbed, and the juvenile newt emerges from the pond onto land.

This also bears out in the volunteer surveys of single samples from 239 ponds that detected great crested newts 91.2% of the time (218 ponds) when they were known to be present using other methods. These levels of accuracy are unprecedented and when you consider there was also no evidence of false positives (eDNA did not record newts where it was believed there were none) or cross contamination between sites, eDNA looks like an attractive alternative!

There was also no evidence that eDNA detect-ability varied during the sampling period (mid-April to early June), either in the detailed methodological study sites or in the broad volunteer survey. Given it’s benefits over traditional testing methods, you can see why this ground breaking technique has been approved for use and supported by Natural England.

In the detailed study that was carried out, the eDNA testing was more effective at detecting newts than individual traditional survey methods (e.g. torch counts, bottle trapping, egg searches) over the course of the survey season.

For traditional methods to achieve similar detection rates to eDNA, it was necessary to combine torch counts and bottle trapping, although later in the season eDNA was significantly more effective than even torch and bottle trapping combined. Torch counts and egg searches combined were not as effective as eDNA in England and only equal to eDNA in Wales early in the season.

Levels of accuracy of detection of traditional methods:

Bottle trapping – 76%
Torch survey – 74%
Egg searches – 44%

Mitigation efforts for great crested newts can be expensive if you find them on a development site, for example one recent case in Milton Keynes a building firm claimed to have had to spend more than £1 million catching 150 of the great crested newts – delaying the construction of 6,500 new homes by up to a year at a cost of £6,700 per newt saved.

Another instance reported was a couple barred from living in £1 million house for a year after protected newts move in after floods – because the great crested newt apparently got there first. However with the introduction of eDNA, testing for them in the first place is now considerably more cost effective, just requiring a brief visit to a pond, significantly cutting down on the number of survey visits need to determine presence absence from four to just one.