In the last century, Worth Forest was famous for its moths and butterflies. "By every account" we are told, "Tilgate Forest was a legendary place for entomologists, and the chance of obtaining fabled insects enticed all of the great national collectors of the day...The heath", after the coming of the railway, "was undoubtedly then the foremost for lepidoptera in Sussex, and its destruction was another great tragedy".
The Kentish Glory moth was the most sought after. It "flew commonly over the heather...occasionally in many hundreds". High Brown and Marsh Fritillaries and Wood White butterflies, with Scarce Dagger, Purple-bordered Gold, Orange Upperwing, Anomalous, Small Grass Emerald, Dingy Mocha and Cloaked Pug moths all flew there. Some of the conditions for this fame continue. Thus, Alder carr and Birch woodland continue to be strong components of the Forest. Tilgate Forest was also "the leading national site" for White Barred Clearwing, Synanthedon speciformis, and it is still present in Worth Forest on Balcombe Down - both of those moths are dependent upon Alder and Birch.
It is at Oldhouse Warren. White Legged Damselfly, Platycnemis pennipes, is on Stanford Brook. There is a large population of Horse Stinger / Golden Ringed Dragonfly, Cordulegaster boltonii, in the Forest, including Worth Lodge, Brantridge and Monks Forests, Worth Forest SSSI, Stanford Brook North and Half Smock Stream in Oldhouse Warren. This is our largest dragonfly and arguably our most charismatic. It flies with Beautiful Demoiselle, Calopteryx virgo, on fast-flowing wooded headstreams. Keeled Skimmer, Orthetrum coerulescens, till recently recorded solely on Ashdown Forest, is present too on Worth Forest (as at Greentrees).
Large and charismatic forest insects present in Worth Forest include Green Tiger Beetle, Cicindella campestris, and the harmless giant Sabre Wasp, Rhyssa persuasoria, as long as a small child's hand. The latter is a parasite of the equally fearsome-but-harmless Greater Horntail Wasp, Urocerus gigas. The huge Tanner Longhorn Beetle, Prionus coriarus, larger than a Stag Beetle but without the 'antler' jaws, is present. These latter species are dead wood dependent and therefore thrive in the presence of mature and veteran forest trees. Glow Worms, Lampyris noctiluca, are present on Balcombe Down West and Oldhouse Warren, and no doubt more widely.
Worth Forest has two strong ancient woodland indicator molluscs. The Ash Black Slug, Limax cinereoniger, has been called "a wonderful judgexviii of scenery" because of her faithfulness to ancient woodland. She is also called the 'Mint Humbug Slug', because her foot is striped black and white. The Lemon Yellow Slug, Malacolimax tenellus, aka 'Queen of the Rain' (because she is mostly found in pouring rain) often particularly occurs amongst veteran trees, hence her other name 'Companion of Ancients'. She is known from Greentrees, Oldhouse Warren and Denches Copse.
The scarce Jet Black Ant, Lasius fuliginosus, also has a close relationship with veteran trees, where it lives a largely arboreal existence. It is found on ancient Beech pollards at Balcombe Down West. Worth Forest has a robust and important population of the only true woodland ant in Britain, the Red Wood Ant, Formica rufa, which makes large thatched, domed nests and forages widely (including in our picnics). In the Weald is its found chiefly in Worth, St Leonard's, and Ashdown Forests and on the western Lower Greensand heaths. Despite both national and local declines, at Worth they are found in Tilgate Forest, High Beeches and Brantridge Forests, Balcombe Down West, Oldhouse Warren, and at The Warren, next to Paddockhurst Park.