Dartmoor Tick Watch
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Why Dartmoor Tick Watch 2009 numbers
are probably under-estimates
This page needs tidying up .....
1. Results depend on sampling i.e. the availability, weather, commitments and willingness of collectors etc.
2. Many areas are not represented
3. Collectors generally overlook the smallest ticks such as larvae and nymphs - this skews results. This is one reason to do a regular sampling “drag” in different habitats:
Ringmoor Down, high open grass moorland
Brisworthy Plantation, a bracken area on the edge of Ringmoor Down
Yarner Woods, with its milder microclimate, throughout the year.
4. The length of the largest ticks is affected by curling under of the mouthparts in highly engorged females – but not in all highly engorged ticks
5. The length of mating males is impossible to measure precisely
6. Collecting results may be affected by recent weather:
Very hot weather can produce diminished results because the ticks go down among the roots etc. to avoid desiccation, also .....
Ticks may go ‘underground’ following very cold weather e.g. winter frosts for a few days as happened at Yarner Wood in December 2008.
Ticks may go underground or seek other shelter during/after very wet weather.
7. Dragging factors
The ‘lay’ of the blanket can be important and how it is dragged – esp. over tall bracken – how much real coverage etc?
repeat checking of blanket at short distance intervals in case ticks drop off again?
“dwell time” may affect time ticks have to reach the blanket. NB – However, most ticks are found on the leading third of the blanket, so dwell time may be less of a problem?
direction and wind – self upwind may provide greater stimulation of ticks where possible.
underestimates populations because not all ticks on top “questing”? Some may be under the leaves, in the ground etc.
12. Suspect most numbers for larvae are underestimates because they are difficult to count or estimate on blankets.
13. Time of day of collecting, normally 10 am to 1 pm. Earlier – more ticks ‘up’? Also, how many climbing up/descending vegetation and not actively questing?
Suspect numbers for all stages are
under-estimates for the reasons given above.
15. RESULTS – CHARTS etc
Total ticks 2009 – useful for an overview of the project's results but there are disparities re. e.g. small ticks i.e. nymphs and larvae …..
because these are not commonly collected by pet or livestock owners because they are difficult to see among animal fur and yet there are probably more nymphs and larvae in the habitat than there are adults.
Also, walkers find more nymphs than larvae, same reason?
Total ticks from KR “dragging” – more valid because all life stages recorded
Total ticks from a habitat e.g (1) Yarner sheltered wood, (2) exposed moorland grass and (3) moorland bracken – these are representative of the particular habitats re. seasonality
Life cycle stages from a particular habitat – indicate precisely what life stages are present on a seasonal basis – BUT may be different next year depending on the weather?
Yarner Wood Y2 area results are all from the same route/path – depleting the population rather than sampling fresh areas each time, therefore under-estimating the true number of ticks? Chosen so as to have the same sample track length precisely each time.
All tick visitors counted by