A bite from a radioactive spider on a school field trip causes a variety of changes in the body of Peter Parker and gives him superpowers.[81] In the original Lee-Ditko stories, Spider-Man has the ability to cling to walls, superhuman strength, a sixth sense ("spider-sense") that alerts him to danger, perfect balance and equilibrium, as well as superhuman speed and agility. Some of his comic series have him shooting webs from his wrists.[81] Academically brilliant, Parker has expertise in the fields of applied science, chemistry, physics, biology, engineering, mathematics, and mechanics. The character was originally conceived by Stan Lee and Steve Ditko as intellectually gifted, but not a genius; however, later writers have depicted the character as a genius.[82] With his talents, he sews his own costume to conceal his identity, and constructs many devices that complement his powers, most notably mechanical web-shooters.[81] This mechanism ejects an advanced adhesive, releasing web-fluid in a variety of configurations, including a single rope-like strand to swing from, a net to bind enemies, and a simple glob to foul machinery or blind an opponent. He can also weave the web material into simple forms like a shield, a spherical protection or hemispherical barrier, a club, or a hang-glider wing. Other equipment include spider-tracers (spider-shaped adhesive homing beacons keyed to his own spider-sense), a light beacon which can either be used as a flashlight or project a "Spider-Signal" design, and a specially modified camera that can take pictures automatically.