Snake-flies, alderflies, lacewings and scorpion flies in Essex
Table 1. Essex rarity categories (Harvey 1998, 1999)
Category Qualifying criteria
Extinct Not recorded in the county for at least 50 years
Essex Rare 1% or less of surveyed monads
Essex Scarce 1% - 5% of surveyed monads
Essex Local 5% - 15% of surveyed monads
Essex Common 15% - 30% of recorded monads*
Essex ubiquitous more than 30% of recorded monads
*Note that Harvey's original definition of Essex Common contained a printing error indicating that 15-25% of recorded
monads was the requirement. This left a gap of 5% between Essex Common (15 - 25%) and Essex Ubiquitous (>30%). The
figures provided above are those intended by Harvey in his original work and 1 am grateful to Peter for pointing out the
typesetting error to me.
Harvey's threat categories were intended to assess threat factors at a regional level, but taking on
board a national perspective. His categories are summarised in Table 2.
Table 2. Essex threat categories (Harvey 1998, 1999)
Category________Qualifying criteria__________________________________________
Endangered • Single Essex population or Essex Extinct but would need
____________________protection il'rediscovered__________________________________
Vulnerable • Only two extant populations;
• Essex Rare species restricted to habitat or sites under known
threat;
• Species known only from sites designated Vulnerable;
• Species exhibiting continuous decline in preceding 20 years and
____________________now in less than 1% of surveyed monads______________________
Threatened • Essex Rare or Essex Scarce species with a Frequency Ratio** of
less than 1.5 and Tetrad percentage of less than 1.0**;
• Essex Scarce species restricted to habitats or sites under known
threat;
_________________• Species exhibiting continuous decline in preceding 20 years_______
Regionally • Significant portion of national population is in Essex;
Important • Species associated with a threatened habitat that is included in the
national Biodiversity Action Plan;
• Species dominant in, or peculiar to, a habitat of which a high
percentage is represented in Essex;
_________________• All Red Data Book and Nationally Notable species______________
Unknown • Insufficient data but which may be under significant habitat or site
____________________threat__________________________________________________
**Frequency Ratio and tetrad percentage have not been calculated in the present paper because the level of recording
coverage is considered inadequate to permit accurate use of these values.
Essex Naturalist (New Series) 17 (2000)
ISI