Tremors 2: Aftershocks

An man on an oil field in Sonora, Mexico flees from an underground creature which emerges and eats the man, revealing it to be a graboid. Years after the events of the first film, Val McKee has moved away and married Rhonda LeBeck, while Earl Basset has squandered his fortune on a failing ostrich ranch. He is approached by Carlos Ortega, who informs him that graboids are killing his workers at his oil field in Sonora, Mexico, and hires him to hunt them down. Earl initially declines, but Ortega's taxi driver, Grady Hoover, convinces Earl to change his mind; both join the hunt. Upon arrival in Sonora, Earl learns that the company would pay him double if he caught one of the creatures alive. He also meets geologist Kate Reilly and her assistant Julio, who are scientifically investigating the Graboids.
Earl and Grady begin systematically killing the Graboids by using remote-controlled cars rigged with explosives. Realizing the vast number of Graboids, Earl enlists the help of Burt Gummer, who arrives with a truck loaded with firearms and explosives. The next day, Earl and Grady encounter what appears to be a sick Graboid after crashing their truck. They radio for the oil field's mechanic Pedro and wait with the Graboid. That night, the Graboid dies, and Earl and Grady find sacs within the carcass. Pedro's truck arrives, but Grady and Earl find only his arms remaining and the engine motor ripped apart. While breaking into a parked car, they encounter several Graboid-like creatures, later named Shriekers, that have apparently come from their Graboid. Meanwhile, Burt's truck is ambushed by a pack of Shriekers while returning to base.
Julio is killed by Shriekers moments before Earl and Grady arrive and kill them the following morning. The creatures attack and they are forced to hide inside the office. Burt arrives, having engaged the Shriekers and captured a live one. Through experimentation, the group discovers that, through eating, the hermaphrodite creatures can replicate at an incredible rate. They also learn that the creatures cannot hear unlike their predecessors, but rather see heat through special infrared receptors on their heads, thus their targeting of car engines. They are attacked by the Shriekers, who chase them throughout the compound. They run for Julio's car, but Burt accidentally disables it while killing a Shrieker.
Hiding from the Shriekers, Burt is trapped in a bulldozer bucket and Grady, Kate, and Earl on top of an oil tower. The Shriekers work together in an attempt to climb the tower before Burt traps them in the storage shed with the truck. However, they discover rice flour is stored inside as well, enabling the Shriekers to continue multiplying inside. Earl douses himself in CO2 from a fire extinguisher to hide his body heat, and tries to find Burt's explosives inside. However, the Shriekers eventually detect him, forcing Earl to throw the detonator among Burt's supplies before escaping. The group manages to escape before the explosives level the facility, destroying all of the Shriekers. In the aftermath, Earl and Kate decide to pursue each other romantically, while Grady suggests opening a monster-themed theme park due to the money Ortega now owes them.

Question: What is Burt hiding from in the bulldozer bucket?
Answer: Shriekers